Can I use cards from the What’s That…, Who’s That… and Where’s That… base and expansion games together?

In a word, yes.

You can mix and match cards from each base game and expansions. If you don’t want to to have video games in a game, no problem just take them out.

You will have however the unique card backs for each game. However, although it may give you a helping hand it would only be slight, and if you play using the rules you’ll have a few cards in hand already so wouldn’t be able to see the back of the card you would be currently looking at.