Scion, heir, child, progeny.
The opposite would be descendent. A synonym might be forefather.
Development of descendent proceeds farther than that of the ancestor so that earlier stages of the descendent resemble ancestral adults.
Width
The sun
The direct descendents of a person are that person's children, grandchildren, great-grandchildren, etc. The direct descendents can trace their ancestry directly back to the person. For example, you are your great-great-grandmother's direct descendent, but you are not the direct descendent of your great-great-grandmother's sister.
The Umayyads
Allegedly he was a distant descendent.
Syphillis
The three toed sloth
Labor Unions
Because he is a descendent of his mother.
Elijah and