How do mutations occur in children that do not occur in parents?

These genetic changes are not present in a parent's egg or sperm cells, or in the fertilized egg, but happen a bit later when the embryo includes several cells. As all the cells divide during growth and development, cells that arise from the cell with the altered gene will have the mutation, while other cells will not.

Explanation:

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.