@NataliaAlianovna_ I personally believe he was too confident in Dumbledore and got overly comfortable within the protections on the home, making him careless. And though they matured a bit since their school years, it's very hard to change so drastically and suddenly become the epitome of father material. So I kind of understand the choice for Peter, who is easily overlooked. They must've not thought it fully through, or never gave the thought that Peter would be anything but less then suitable in any way (since of course, they are best of friends). All in all, I just think they had too much trust on Dumbledore, who in the end let them all fall through his fingers. One way or another he failed them, and they failed each other.