I have used an Ant Farm in the past as a class pet for my first graders. They are very co-operative creatures and when you get them via the mail they only send you the worker ants.
No queen or soldier ants are allowed to be sent. Feed them and add water to their "nest" once or twice a week and that is basically it. I often kept them covered up as I found they did more digging this way - in the dark. Then I would have various times when small groups could go and take the box off and observe the ant farm with all their tunnels. I do prefer the ant farms that are thin and tall and not the hill like ones out there but either would serve the purpose.
I had planned to do one this year as well but wanted to wait until March or April to order them via the mail as it gets very cold here. I might order them right away and have them come in September but will have to bring them straight home at Christmas and get them into a warm house. Cold is not good for them although I have never needed heat lamps or anything like that, just a warm room temperature and they are good to go.
I had tried last year to order ladybugs but was told that they are a pest and could not order them and bring them into Canada. The K teachers do butterflies and then let them go and I was hoping to do the something similar in May or June. I'll have to look and see what is available but will probably just stick with ants.