Keep it simple.
Just kidding! Well, not really. There are lots of reasons, and this is just one, and certainly there are those who have kids that keep homebrewing. But I've known a lot of homebrewers that are very much invested in the hobby, but then, quite understandably, get much more invested in their new family members. Time gets short. Budgets get tighter. Sleep becomes a rarity. If you know someone who's running really short on time thanks to their new addition(s), maybe offer to do a team brew with them, pick up their ingredients on your next LHBS run since they might not be able to get out there, and just be a supportive fellow homebrewer. And you might also remind them that they're now responsible for training the next generation - my friend Seth's son Gabe got, as a Christmas present, one of my old CO2 regulators. That kid is seriously into brewing, and he's not old enough to drink for another decade and a half.
Really, this time - Keep it simple.