When are puppies sturdy?

That is not phrased very well. What I am asking is - I'm getting a new puppy, she will be about 9 wks old when I get her, St. Bernard puppy so she will be at least 20 lbs, probably more when I bring her home. Indy is going to want to play with her. He is a BIG boy (31 ins tall, 100+ lbs - haven't weighed him in awhile) and he plays rough. He is also quite clumsy. I don't want him to accidentally hurt her b/c I know how puppies can get up under feet and I don't want him to crush her. Soo.....about when should her bones be solid enough to have them play without me worrying? if that makes sense?

 

you will need to supervise them and not let them alone for awhile, fo how long I dont know. I would think yo dont want a lot of rough housing for a few months if not more, so hopefully someone else can best answer this