Kids are always going to want to continue with practice at home. It's good for them and it's fun. As long as they stick to basics, and never use incorrect equipment, it's okay. Bars is a concern, and should always, always stick to those basics. Beam, jumps, cartwheels, maybe even walkovers at home later on, but still sticking to the basics. Floor probably is where they can stretch the rules a bit, as long as the mat is nice and soft, and they don't make a habit of trying to learn skills. Learning skills at home is a big danger, so make sure to prevent that. In the end, it's up to you to enforce what they can and can't do.