The Revolution applied by the vet would have effectively killed any fleas left. Fleas normally will not go too far away from their available food source so if they were confined to one room (good for introducing to older cat btw) and you have since cleaned the room I would not be too concerned.
Did you contact the shelter and tell them the kittens had fleas? If not please do so so that they are aware.
I really wish shelters would not find it necessary to separate the mom and her kittens at such a young age. Ideally they should be with mom until at the very least 8 weeks. 10 to 12 is better. They learn so much from mom during those weeks.
Have fun with your new babies. Now would be a great time to get them on a good quality canned food and dump the dry. www.catinfo.org
- great reading!!