It's not a bad idea to get your kids involved in aerobics, even if they don't need it for weight loss. Why? Because kids raised in an active family are much more likely to be active later in life, when it counts. Activity doesn't just help in the short run, it sets a good example for the future.
Your aerobics teacher should always incorporate warm-up and cool-down sessions into the class, before and after, respectively. In addition, stretch slowly and carefully before class, in order to get your muscles used to the idea of the upcoming strenuous activity.