What are the symptoms of synesthesia for kids?

Well, they usually say things which sound for them obvious, but they are not. such as:

This house smells pink.

How come when 2(blue) + 3(yellow) equals to 5? (pink)

I like this looking at music. i specially love <enter random song> because it has light blue colors.

I don't like chicken. it has pink color, and i don't like pink.

I don't like Dark Chocolate. It has peanut butter smell.

I don't like ice cream. it has a bad sound.

there are too many of syns to check all of them, but usually, just ask him/her what he/she see.

They will discover it themself. usually it gets discovered at 10-12.

Good luck!