Even though this is for large fish forum I do also have a little 'for kids' view type of community fish, I'd say go for a 10-20gallon as it's too little for a school of fish which is quite popular in the hobby. But if you might well ask, go for corydoras, they're great at eating algae and do their thing best, might as well put a betta. Yep, pretty much that's all I can give.