I would keep her a little longer since your vet says the fontanel is pretty big.You can teach small children not to be rough ,however some kids don't listen and may sometimes think they are playing with the dog but accidents happen if kids this small are around a pup so small. I have two daughters and my daughters were 12 and 6 1/2 yrs old. I was extremely strict when it came to our yorkie that was around 1lb 4 oz when it came home. Kids drop them all the time. I have children visit all the time and I have the hardest time trying to teach little boys not to play rough with my little dogs. I usually keep my dogs in my bedroom if small children are in my house.
I would not be terribly worried about the open fontanel . These things often closeup a bit more within 6 months.
Just speaking from my experience.
I would love to see a picture of this little furbaby!
Genie, Cookie & Lola |