With this fabric pattern, I can see it working as daytime pants. Some ideas to make it more “daytime appropriate”- ruffles at the bottom hem instead of a hem binding, a “mock” fly in the front, cargo pockets, side pockets, back pockets, knee patches. I also have a niece about this age (a little older) whose favorite thing to wear to school is P.J.’s. They’re officially “banned” at school, but she delights in bending the rules because they’re homemade.
My kids all love the P.J. pants, and they scout the fabric stores for fun fabrics for me to use for this pattern. (So far we have soccer balls, Hot Wheels, rockets, Olivia the Pig, Thomas the Tank Engine, butterflies, etc.) Have fun with it- I’ve found this pants pattern to be very easy to adapt.