Formal:
* Children
* Youth
* Minors
* Offspring
* Progeny
Informal:
* Little ones
* Tiny humans
* Youngsters
* Brats (not always positive)
* Munchkins
* Tots
* Sprout(s)
* Kiddos
* Little ones
* The wee ones
More specific:
* Boys
* Girls
* Babies (for very young children)
* Teens
* Pre-teens
The best word to use will depend on the specific situation. For example, "children" is a more formal and respectful word than "kids," while "brats" is a more informal and sometimes negative word.