My son downloaded 2 Monster High audiobooks to his iPadmini, but we can't figure out where to play them from? Help please.

I've seen that you've found them, but note also that audiobooks are currently a one-time only download from the store, so you may want to copy them from the iPad to your computer's iTunes via File > Transfer Purchases (File > Devices > Transfer Purchases on iTunes 11) so that you can take a backup copy of them - they should copy over to the Books part of your iTunes library.