@boatass Well bloody said. The OP has made a grave error in judgement, there's no need to tar and feather her for it. She's trying to put her kids first, no one can blame her for that. If you are doing, have a good look at yourself, she came for some support.
I am a dog person through and through, but I am also a mother and if I was frightened for my kids, there's one solution, the dog sadly has to go.
OP, you made a very naïve thing but it's the mature thing to hold your hands up and say this isn't working, she deserves a home where someone can manage her appropriately and safely.
I think the main thing you can do, is try and be as confident as you can. See the behaviourist and listen to what they advise, you've had some good advice on here, especially with the muzzle.
Try it for a couple more weeks and see if there is an improvement, get signed up for training if you can.
If the situation has not improved, or deteriorates any further during that time I think you have to make the hard decision to contact the RSPCA or another rescue centre.
You need to cool off getting another dog for a few years and do not buy from an online site again.