Self-seriousness is exhausting.
You play better when you play loose. Self-seriousness makes you play tight.
One of the best things about kids is that they are weird and random. When confronted with a weird kid doing something random, it tends to shatter self-seriousness (unless you’re in a really bad way that calls for time alone to get your shit together).
Being around my kids in the morning before I start working is a great way to loosen me up for the day. Their random requests, jokes, and antics are just too delightful to keep me tight. (They can be annoying too. I’m not trying to over-romanticize this.)
Comedy can do this too, but adult comedy tends to be cynical and can cause you to dig into the self-seriousness. There’s something about the non sequiturs from kids that prevent any pretention or cynicism.