Yes, HOBBYHORSES is a Scrabble word!

Letter values in Scrabble US: H 4, O 1, B 3, B 3, Y 4, H 4, O 1, R 1, S 1, E 1, S 1.

Is it a valid word?

HOBBYHORSES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a topic to which one constantly reverts
a child's plaything consisting of an imitation horse mounted on rockers; the child straddles it and pretends to ride

Also: rocking horse.