Two quick-and-dirty nuts-and-bolts things. First, if you are addressing a character by name, the standard formatting includes a comma before and the capitalization of the name. An example:
“Would you like this disgusting tennis ball, Gertie?” (My dog’s favorite question.)
Second, if the character happens to be the parent in your story, you need to make an important distinction. Are you addressing them as Mom or Dad (as if it is their name), or are you referring to them as a noun? I see this all the time in manuscripts. Here’s an example that makes the distinction clear:
“Do you have a mom, too, Mom?”
Here, you can talk about “a mom” or “her dad” or “his mommy” all you want, but it is lowercase. The second you use it to address a character, just as you would a name, it becomes capitalized. A quick proofread will tell you if you’re on the right track. If not, commit this simple rule of thumb to memory.