There's another factor at work, I think... its that J is an "only" child.
Now, with Pup around, he's no longer the "only", and also not the "littlest".
It should be easier to curb the "out wandering around" thing, because Pup needs J! And its much easier to get compliance with a carrot than with a stick, as they say... also easier for J: instead of "Mom won't let me" he can say "need to look after my dog".