I think first grade music of children is folk songs they have been taught like coming round the mountain and campfire type songs from camp/scouts...like on top of spaghetti type songs. Rafi songs are good for this age (baby beluga, down by the sea, There was an old lady who swallowed a fly). And hey every time I make fruit salad I burst into the wiggles and I am nearing 50 years old.

My ten year old did like kidz bop CDs starting around age seven or eight. And he likes Disney pop from about that age.