I agree. I think 30 days is sufficient for most dogs. You say you're worried about if he doesn't work out & you have to return him, but really, if you 'foster' or 'trial' him & he doesn't work out, you'll have to do the same thing.
Our son is 7yo, autistic, exceptionally loud, pretty bouncy & fast, etc. We've learned he generally brings out the opposite in animals (if they generally like kids, they hate him; if they typically don't like kids, they love him) so we'd decided to adopt a puppy for him when he was 3yo. Bo did wonders for him in every way & our son has come so far it's hard to imagine how he used to be just 4yrs ago. But unfortunately he just suddenly ruptured a disk in his lower back- this on top of his congenital shallow hip sockets that were drastically degenerating, & plano. that popped up anytime we took a vacation (with or without the dogs) & his overall huge size. At 4yo, his activity was already pretty restricted to keep him from getting hurt while playing, & from the day he came into our home at 8wks, he was OUR SON'S dog, he could care less if we even existed & it took 2yrs before he sought attention from me himself. All things considered, I made the very hard decision to put him down instead of him living in even more pain (if he could recover) & having an even more restricted life that would basically keep him from his kid. I couldn't do it.
Our remaining dog, 11yo couch potato, hadn't been an only child for the last 10yrs (his "sister" died of bloat shortly after we got Bo) & was slipping back into his CRAZY separation anxiety quickly. We went on the hunt for an older dog that would be happy lounging on the couch & being loved & spoiled.
After looking around, we kept coming back to Odie, a 10yo small hound mix that was picked up as a stray. He'd been at the shelter for 2mo & no one had taken him out for a visit until we did. Well he perfectly clicked with our old guy & we took him home, I still keep an eye on our son (because I always do with kids & dogs- period) but he's adjusting beautifully. We knew all his quirks in the first 30 days. We introduced him to anything he may come into contact with in our family & just observed him in general. We've concluded he was definitely used as a deer-hunting hound, possibly a bird dog too, he's mostly tone deaf, he'll put up with anything you do to him but he isn't very comfortable at all- but let HIM do it at his own pace & he's perfectly happy. Not to mention lots of little details. Only thing we learned after 30 days was it seems he may have been beat with a stick of some sort.
Most shelters & rescues request, or have in their contracts, that if the dog ever has to be given up, that it's returned to the shelter/rescue it was adopted from. I don't see how a 30-60 day trial is any different than a flat-out adoption if it doesn't work out in the end, or if it does. Either he stays or he goes back, yes? All the same considerations are in play- I would keep kids away from the dogs at feeding time- until you're sure how that goes, & strict supervision with them with toys/treats. Outside of that, if the kid & dog get along well at first, general safety & supervision are all you should need to figure out if he'll work or not.