Need help with a Dog

So this a bit of a long story, but the short version is my family adopted a dog. A small lab who was and is mostly sweet as can be. We had play dates with her and the kids, and finally picked her up Monday.

She was the sweetest, most timid little black lab.

This was a pretty big deal for our family and something we were excited about. A few months back we lost a dog we had had for 14 years.

Monday, the kids get home from school and She began to nip at the kids and gotten extremely protective of our home. She only acts this way to the kids. With my wife and I she's as sweet as can be, she listens, and just seems fantastic.

However, we simply can't keep a dog we can't trust with our kids. I would hate to take her back to the shelter but I'm at a loss for options. Is there any dog rescues or other options for her?

The whole situation is just terrible and I'm at a loss for options and not sure if there are other resources available