Are there any activities here that are specially geared towards a 5 and under age group? For example our local science center has an “iExplore” section that has a lot of hands on play (a huge light bright board, rice pit, water painting, etc)

There are plenty of things for that age group. Almost every thing is hands on. And what's the best is that they have enough things to do that kids aren't just standing around waiting for their turn.

3-5 yes, there's a kid's room with crafts behind the biomes on lower floor. Btw - the Cal science center is free

There is a small play area. There is an aquarium.