We don't all play the game the way EA/Maxis intended it; sometimes we change the rules and create ourselves some new challenges. If such a challenge involves playing a house with ONLY children, then suddenly, one can no longer have pets. They get taken away by the Animal Control Officer, regardless of how well the pet is cared for!
I found out why: there's no human sim of teen or older age present! So now, in response to a request by MysteryIslandKid
, I changed the rules to accept even children (but not toddlers) as suitable caretakers. The ACO will come no more... at least not for THAT reason