I'm looking for a unique made-up super power

The kids going to be Gay as a goose 🥹

The power to accurately predict when the next bus will turn up.

what does that have anything to do with the parents' superpowers?

I accept it's not as straightforword as being gay as a goose, yet their Mary Sue powers are pretty spectacular so you need to up it.

Considerably.

Bus prediction is way more uncanny than their parents ability.

One of my work colleagues once described the Hampshire bus timetable as the greatest work of fiction in the English language.

That's what.

The kid will be able to transform into invisibility to get away from
parent 1 projecting himself and parent 2 who takes over bodies.

An ability to yell out random numbers on command.

How about like a porcupine having killer needles that you can shoot out or like a skunk that you can fart out so strong that it causes other to be immobilized.

Both parental powers have to do with body alteration/movement. So why not give Junior something kind of in the middle, like the ability to tag people with various trackers (not tech; I mean like a hormone or the like) and have those people be irresistibly drawn to each other? It doesn't have to be for romance. It could be to get a criminal to make a beeline for their tag 'twin', the janitor at the local jail.