Try a prevue 528 cage. I have this one. No escapes thus far, and very sturdy. It's a good size for 2-3 mice. (3 max) By the way, I would recommend getting 3 mice, as the group dynamic is better, and you have the added security of if god forbid one should unexpectedly die, you don't want a lonely and sad mouse. Also, please don't buy from pet stores. This is something I wish I researched before getting my girls. They're often sickly and have bad genetics. Also, they're bred in conditions similar to puppy mills. Forgive me if you already know this. Thanks for being responsible and providing good care! I'm sure you're going to be a parent that responsible takes care of the pet. (because obviously seven year olds aren't going to haha) Also, I have a subreddit, r/RateMyCage, where you can post your setup when you get your girls :)