The other thing you could do (which I occasionally do with children pupils) is to take a very well known tune (God Save the Queen, Happy Birthday are my usual candidates) and play it with a very strange rhythm to see whether they can recognise it.
There's a sight-reading book called 'Hidden Tunes' that consists solely of well-known melodies (carols, Greensleeves, National Anthem, Happy Birthday etc) notated entirely without time signature, bar lines or rhythms. Just the pitches written in semibreves. The titles are also not given and the fun part is to work out the identity of the tune. It's strangely difficult and rather addictive.