LadyMisha -- I'm chiming in late, but I just wanted to let you know that I think you are marvelous!

Both for taking in the pup and allowing the child to come over and play with puppy.
When I first got my Daisy (a rescue rot) I.did.not.want.a.dog. but LDH and DDs persuasion was heavy. It was mostly Daisy, herself, that grabbed my heart. The foster parents brought Daisy to my home for a visit, discussion, see if we were a good fit. As soon as that dog walked into my home, she came right to me. She wouldn't leave my side.
There was no way that dog was leaving
my her new home.
I like to think that Daisy found me . . . just like your puppy found you.
I knew nothing about dogs. Never had one. What do they eat? How much do they eat? What do you need to look for as far as sickness? How often do you take them to a vet?
I was in my 40's. I was thrown into a tizzy about how to properly care for/train a dog. I did a lot of on-line research. I can't imagine a 10 year old figuring out if the dog needs to go to a vet or not. The DDs knew to clean up the yard, give Daisy food and water and give her plenty of exercise. That's about it. They learned with me whenever we took the dog to the vet. I had no clue about heartworm meds, etc.
I agree with the PPers that said it's not the child's fault.
I also agree with the PPers that said OP is doing a good deed by letting the child come over and play with her puppy. She will be able to teach him a few things about the responsibility of animal ownership.
LadyMisha, this puppy found you because he knew that you needed him and that he will be loved. Kudos to you!

P.S. How old is Rocky? Would you please provide a link to your previous thread?