I would definitely buy such a pack but I think in principle it should be part of an occult pack.
It should not be a stand alone thing but somehow tied to the adult version. Perhaps like fame in the sense that children can get fame up to a certain level and the top levels are available once they become teens.
I am definitely not against dlc for dlc. If it is done properly. I think it is a shame my first pets stuff ruined the chances for future dlc for dlc because of the bad reception. It had a few bad design choices (furniture sets split up, majority of clothes are just recolors,...) but there is definitely room for dlc for dlc in my opinion.
