Okay, imagine you have a really cool toy that tells you the time! That toy is like a wristwatch. When we say, 'He has no problem playing with his wristwatch on,' it means he can have fun and play games without taking off his wristwatch.
Sometimes, when we wear something like a watch, it can feel a little funny or get in the way. But this boy doesn't mind at all! He can jump, run, and play with his watch on his wrist, just like it's part of him. It’s like when you wear your favorite shirt; it makes you feel good, and you can play happily without worrying about it.
So, wearing a wristwatch while playing is totally fine, and it can even help you know when it’s time to stop playing and have a snack!