Not bad so far. This is just from looking, It seems the bell does not have enough detail. and that the legos Seems to be too highpoly. I would try and fix that first before adding the walls like Mrchronos said. Also remember you have stuffed animals, woodentrains, and blocks to work with. Also I would do research on what modern toys look like as well because it could resonate with some of the younger kids. I would try to unwrap stuff before hand.