To quote my coworker, Shane, "Get it in Focus. I can fix almost anything else in editing."
But things start getting a little more complicated when we talk about how we control what is and isn't in "acceptable focus" within your frame.
For a lot of people, getting any more complicated than Autofocus is as far as they will ever choose to go.
Firstly, allow me to shout it from the rooftops, AUTOFOCUS IS NOT A SIN. It's not unprofessional, it's not anything that is bad. There are some shooting scenarios when it's not appropriate, but for 95% of the shooting that you might be doing in and around the parks, it is your best friend. Autofocus has also gotten insanely sophisticated over the years, so I highly recommend you refer to the user manual for your particular camera and see which TYPE of autofocus is most appropriate for the shooting you plan to do (yes, there are different types of autofocus on each camera). The more expensive the camera, the more focus points and focus types you generally have available.
You can also adjust, on the fly, where the focus point is within your monitor (on your viewfinder, it's the little spot that tends to blink/get solid/ (hopefully) follow the thing you're trying to get in focus. So being mindful where your focal spot is? Super important. Then keep a conscious eye on it WHILE you are shooting. Or you'll get home and find a lot of photos where your camera focused on the wall of Fairytale hall instead of your kid's beaming face.
But... wait how did that happen? The dot isn't choosing an area within a 2 dimensional frame to put into focus; it's choosing a point on the perpendicular axis to bring into focus. For example, if you focus on your subject's eyes, and their eyes are exactly 1 meter from the camera, ALL OBJECTS that are 1 meter from the camera will also be in focus. This is called "focal distance." A lot of zoom lenses don't have markings on the focus ring anymore, but if you look at a prime lens, you'll see a listing of measurements that range from, say, a fraction of a meter out to infinity.
So what, beyond the little dot, determines what's in focus? You have two additional factors to take into account: Depth of Field and Shutter Speed (motion blur).
We touched on Shutter Speed previously and how it affects exposure (which is important!), but it also has a very large effect on whether or not things will be in focus when dealing with a moving subject (or camera). The longer the shutter is open and exposing the frame, any movement either in front of the camera or OF the camera will no longer be sharp. This is why, when dealing with a moving subject such as a parade or show or (ahem) a kid that doesn't necessarily hold still for photos (hi, I love candids), I aim not to go below 1/125 second. IDEALLY 1/250 is safer. But choosing a shutter speed can also be an artistic move. You have an athlete leaping through the air and want every part of their body to be in sharp focus while it flies? You NEED a fast shutter speed. But maybe you have a dancer, who's going to be mostly stationary but their skirt is going to spin around them. There are medium shutter speeds that will keep your dancer's body in focus but the ends of the skirt will blur, etc. (whatever object is moving the fastest in the frame is the first to go out of focus due to shutter speed).
His body was static enough for 1/320, his arms were not. Notice how the blur is more noticeable the further down the arm you look.
You also have to take into account the lens you are using as well as what your camera is doing. If you have a tripod and a very static subject (not PEOPLE, no matter how much they think they are holding still, they aren't) such as a landscape, shutter speed can go back to being exclusively about exposure.
That's how people can capture images of Disney Fireworks and their long trailing streams of light: they are shooting on a VERY long shutter speed on a tripod). Some lenses have advanced image stabilization options (on my Nikkor lenses, my more expensive zoom lenses feature the VR button). It is a WONDER, with the only downside being that it can drain your battery a bit faster than normal. I've had acceptably in focus long zoom shots of Hocus Pocus that I've accidentally let slip down to as low as 1/60 or 1/80 thanks to that VR image stabilization. Still, I would NOT recommend trying to do that for all of your photos; you'll end up with more trash than treasure.
Now, my friends, it's time we take a little trip down the rabbit hole of photography. I've been teaching for almost 10 years, and I know so many students who never FULLY grasp how Depth of Field works. I'm going to do my best to explain to you how DoF is managed and utilized, but the best possible thing you can do for yourself is to take these basic concepts and get out and SHOOT with them in practice.
Depth of Field is a term used to describe HOW MUCH AREA on the perpendicular plane in your photo frame will be in focus. For example, If you're pointing your camera at a Bubble Girl in Festival of Fantasy Parade, you might have a SHALLOW Depth of Field that only has her face to the back of her head in focus. OR you might have a DEEP Depth of Field, where the Bubble Girl as well as the performer behind her are in acceptable focus. You can also go to extremes with Depth of Field, with it being so shallow a person's eyes are in focus but their ears are not, or so deep that a person as well as their background/ the sky are all in acceptable focus.
When you are utilizing the focal distance concept I mentioned above, the point that is being put into focus represents the CENTER of your Depth of field, with acceptable areas of focus extending an equal distance in front of and behind that subject. What is changing when you alter your DoF is HOW FAR from that center point that area of acceptable focus reaches.
So what controls how far that area of acceptable focus extends from the center? Well... there are a LOT of factors, but the biggest and most important is your APERTURE (iris). The relationship is simple enough: the smaller your aperture is, the deeper your DoF will be, and vice versa. SHALLOW DoF will have a large aperture like a 2.8, DEEP DoF will have a small aperture such as f11.
When it comes to choosing an aperture for a particular shooting scenario, I tend to stay within a particular comfort zone that's also at least partly dependent on which lens I'm using that day. If I'm shooting candid portraits indoors of my kid, I'll probably err around a 5.6. If I'm shooting outside for a fast moving subject in full light, I'll probably shoot at least an 8. BTW- shooting at a VERY small aperture, such as f16 or above, is generally not recommended if you can help it. The Depth of Field becomes so deep it will start to pick up the inevitable flecks of dust that are hanging out on your camera's sensor and lens. No, really.
There are many other factors that can influence the appearance of your Depth of Field. For example, how far away your subject is from your camera and/or their background. Subjects closer to the camera will make the DoF appear smaller, as will having the background farther away from the subject. Subjects far from the camera will have less separation from their background and not have as much of an appearance of differentiation with DoF.
There's more to it. OF COURSE there is. The size of the sensor in your camera will also contribute to the appearance of your Depth of Field. And more things. MORE THINGS. But this is enough to get you started. Because in our next issue? We dive deeper down the rabbit hole into FOCAL LENGTH!!! *GASP* and all it's myriad effects on an image.