5 month old puppy barking, growling, snapping at kids – but loving to us, what to do?

First time posting, hope this is ok.

We brought home a puppy yesterday who absolutely melted on my wife's arms. She's very sweet and loving, and smart. After one day I've taught her sit and stay. And she seems very low maintenance in general.

But she's been snapping, barking and growling at my kids (5&7 year olds). She honestly seems like she doesn't like them – she hasn't spent all that much time around them yet.

Our older pup died a few months ago and my kids aren't used to this kind of behavior. They're scared and seem to be constantly concerned about the dog getting out of the area she's in.

We have a ten day window in a foster to adopt situation, so the wife and I aren't sure what do. We can't have our kids frightened to be in their own house. Even as I type this my kids walked in the room and she started barking (she's in an enclosed space with a crate.)

Any suggestions as to what to do? Is this permanent?

She's a mixed terrier, not sure what else. Perhaps a beagle.

Thank you.