I think I'd make a big cake out of eight smaller sections - something like a caterpillar maybe, where each segment of the body is a round cake (cut a curved bit out to make them fit together), and you can put a child's name on each section. The head and the tail can be bonus sections. Two candles on each section - they take turns to blow them out (or all blow out together).
My ante-natal group are having a joint 2nd birthday party for all our children, so there will be eight two year olds. I'm trying to think of a design that will be large enough to enable them all to blow out the candles at the same time, if anyone has any suggestions I'd be really grateful. It's a mix of boys and girls, so preferably something unisex.
A snake? Caterpillar? Something involving individual cupcakes?