In his most recent column, Keith Giffen pointed out a few things he considered "NOT QUITE JUMPING THE SHARK, BUT CLOSE," and two of them were the recent additions of "sons" of both Batman and Superman. Whether you agree or disagree with Giffen, it reminds me of the fact that both characters were introduced already as children. This made me think back to other children of superheroes (who were shown born in the comics) - and the list of children who were NOT killed/prematurely aged is quite slim.
While certainly, from a writing perspective, it is a lot easier to write a child then to write a baby/toddler - but is that really it? It's easier? Is that the reason writers always seem to try to avoid writing growing children? Or does the whole fear of continuity explain it? Children aging means characters have to age, while children prematurely aging - that allows growth without having to age their parents. Still, it's strange how practically universal the avoidance of aging children is in comics.