Learn to take responsibility of things that matter to you. The idea of making a song or poem with your key-phrases is awful honestly. You have three wallets as you mention OP, so are you planning to make three songs for them, what if you mix up the key-phrases? What if the kids mix up the words?
But my main point is, you can make songs about your key-phrases and teach them to kids, while you can write them down, find a safe place to store them. For me making a song and teaching it to kids is more hassle than saving the key-phrases in a safe place.
I agree since it's just too much of a work to do plus making a song about seed with added words will eventually mixed them up and might be forgotten or the kids would completely mix up the words. It's a total disaster for OP to plan like that but at least some of us have some ideas we share in order for OP to get some it while trying to balance which is the best idea for storing seed phrase.
On the other note, what if someone ask the kids what are they singing because it sounded unfamiliar to them then the kids would tell them that it was some random or let's just say their uncle or something teach them this song and then someone trying to solve it thinking that person was into cryptocurrency?