I would not worry too much .....the deed has obviously been done!! I assume this will be her first litter? I am expecting my farm cats to have kittens, as they were visited by tomcats around the same time as your Snowball. The only thing I would say, is keep an eye on her nearer the time as cats are funny creatures, and may already have planned where to have the kittens, and it probably won't be the drawer you have kindly sorted out.
Most of my cats produce 5 or 6 kittens, so get really enormous, and the last few days can hardly walk. I watch for their tummy "dropping" which means the birth is pretty close, and then shut the cat inside. In the past, I have had them go off under sheds and have the kittens, and there was nothing I could do until they were three weeks old, and came out themselves!
It would be better if you could put your drawer somewhere quiet away from the children, at least until the kittens are born. You will be busy with a litter of kittens and the children too.
I am sure your cat will be fine, and there is no need to have scans etc. You will have to post a pic of your kittens!