My experience is with the violin but lots will transfer... Play them in as many ways as possible: like a spider, elephant, snake (etc), angrily, dreamily, creepy, grumpy, surprised (etc etc), getting louder, quieter, etc. (This will automatically use lots of different articulations - staccato, legato etc).
Play them with a rhythm from a piece they are learning (that rhythm on each note - i.e. if playing 'happy birthday' and scale of C, 'happy birthday to you' on C, 'happy birthday to you' on D etc etc - this is really useful on violin, maybe less so on piano???)
Make up a short piece or phrase only using notes from the scale (and on the piano I guess using the same finger patterns if possible). Even better if that piece has a mood or style linked to a piece they are playing.
I also like asking students to say the letter names (easy up, less easy going down) occasionally (can time them and see how fast they can say them).
Hope that helps and that you'll get some more piano orientated ideas...