Time in the Dimension Z passes differently, and Arnim Zola’s son would grow to preteen over the first five issues of Cap Volume 7. Cap, due to his super soldier serum, doesn’t age at all. But he does grow a beard. Cap is raising the boy as his own, forming a paternal bond.
I know lots of people hated this run, but I loved it. It was so different from anything else that had ever happened to Captain America. Plus, I usually find Rick Remeder’s writing to be pretty sterile, but this story felt very true at its core.