Use a basic plain cake recipe and bake it as cup cakes. Then you could have the kids decorate the cakes (with the whole nine yards of decorations) to their choice. Also, you could divide the batter add different colours of food colouring to colour each batter. This should be so much fun for kids. I've actually done this myself. Another idea is to add a piece of fruit in the batter after it's poured into the cake cup.
The very simplest one for kids is easter nests-
Melt some milk chocolate in a bowl over a pan of hot water, Get the kids to break up shredded wheat and stir it into the chocolate. Spoon it into paper cases, put a couple of mini eggs on top of each ( and a little fluffy chick if you want ) and there you go!
Easter Bonnets! - use chocolate digestives for the bas and marshallow teacakes for the tops. With biscuit chocolate side up fix the teacake on the centre using a little blob of icing or melted chocolate. Pipe around the seam between the teacake and the biscuit to form a "hatband", finish with a few small sweet confetti flowers.