OK, This is where it's time to get honest. A toddler is not going to properly care for an aquarium. If the toddler understood the work involved and had the capacity to realize that this would interfere with Spongebob, or Dora, they would never agree to it. The point here is that you want your kid to have a fish tank in their room. There is nothing at all wrong with that. I would go along with the 10 gallon tank. You could even get the Spongebob aquarium set for the child. I would let the child pick out everything (except when there is a compatibility issue). My kids actually have 2 tanks in their shared room. My 10 year old helps me out, and has learned so much about the hobby that it scares me sometimes. My 2 year old daughter likes to look at the livestock, and that's about it. Just make sure that you understand that you are going to pretty much be the only one that takes care of this tank.