I'm crying as I read this because I know the pain you and your family is feeling. Having a dog for 15 or more years...it's soooo hard to let go.
You know you did the right thing, but it hurts...it hurts real bad. And not only do you have to live with your grief, you see your kids hurting and that is so hard as a mother. I feel you.
May your baby rest in peace. I'm sure he had a great life living with you and your family.
I send you great big hugs from me and my crew