fully grown adults are much larger in size than young children what happens to tge cell of the body during the growth of a child

While a child is growning there cells inside of there bodies duplicate, which makes the child grow. This process is called mitosis. Inside a child cells duplicate causing more then one, which causes a child to grown.

Definition of mitosis:

The process is cell division by which the nucleus divides, which consists of four stages, Prophase, Metaphase, Anaphase, and Telophase, and normally resulting in two new nuccules and cell, each of which contains a complete copy of the parental chromosomes.

That basically means a cell in a child body reproduces, and makes another cell which would be the offspring. So the offsprings would have the chromosomes. (DNA)