Children, as per statutes, are individuals below the biological age of 18.
(Children, going by its etymology refers to an unborn or newly born person. (In old English _cildhama_ means womb and literally 'home of the child'). Then it was referred to persons before attaining biological puberty. To use it young adults, hence is perhaps odd. Terminological inexactitude, as Churchill would say!).
Indian Penal Code/ BNS clearly distinguishes between Ages 0-7; 7-12 and 12-18 with regard to culpabilty but do not use terms such as kid/toddler/ grown up child. This lack of terminology is a deficiency that can one day be removed.