A joke is when you get a laugh. It can be a look, it can be starting to talk, then stopping, a double take or calling a boy a girl.
Jokes can fill in a blank spot. (Did you hear the one about the priest the minister and the ....)
If you're over 30, you said Rabbi! In your show, is there an obvious place kids shout out? Make it into a joke. (I need to find the....) kids will shout out rabbit, birthday boy, etc.
Then you twist it, right "my car keys"
Jokes are simply the shock of expecting one thing and something else happens. "The rug being pulled".
If you know this structure, put in a slow burn on purpose. Put in a look of confusion, lead the kids with a verbal cue, let's go sing around the ... right... old spare tire.
This takes a bit of examination but you can get more laughs per show.