Stick Song by Hey Duggie.

Amy Lee has a whole album of kids music inspired by her at the time toddler. Dream Too Much being the lead single.

Postman Pat Theme (the original one from thirty years ago).

Wipeout by The Surfaris

Most Disney songs, especially from Jungle Book and The Lion King. Frozen is also super popular. Oh and We Don't Talk About Bruno.

What Does A Fox Say by Ylvis.

Daddy Cool cover by Placebo.

That song by Fast Food Rockers.

Barbie Girl is really popular despite inappropriate lyrics.

Kids aren't too fussy. You could literally play them Child Prey by Dir En Grey and they'll start dancing if they're already used to hearing rock music.

Just avoid anything ominous sounding, long and progressive (most prog) or with loud sound effects like Blip by Sophie (my niece hated that one).