I don’t remember where we first read this parenting advice, so I can’t guarantee its scientific backing, but here it is anyway.
When your (hypothetical) six-year-old child is talking and singing to himself in bed at night–after you’ve put him to bed–as long as he’s not keeping his (hypothetical) siblings up… let him talk and sing.
Why? Because he’s processing his day in the ways he knows how. And if this (hypothetical) six-year-old son is in all-day kindergarten this year and has just moved this summer, that processing time is important to his development and well-being.
So we let our (not hypothetical) six-year-old son talk and sing after we put him to bed, as long as it’s quiet, and as long as it doesn’t go on for more than a half hour.
More times than not, he’s done in about 15-20 minutes and then fast asleep. And we haven’t gotten upset or into a verbal struggle with him. And–most important–he’s had some added processing time before he goes to bed.