I have aging turned off and play rotationally on my main game, but when I was playing a legacy and everyone was aging , I would just go into households and add children to families.... every once in awhile I would go back and combine young adults into families, and add children. This way there were plenty of people growing up with each generation. I would take someone like Alexander Goth (when he became a young adult) and combine him with another person who had become a young adult, add children, teens etc. to the family, and usually left the older adults in the household too.