Long story short, there was an openning in my attic, and a about a week ago we started to hear meowing. We cuaght the mom with intentions of finding all the babies and taking them to the shelter. However, after catching the mom we couldn't find the babies in all the insulation. After several hours we knew they needed to eat so we let the mom go. Once she reappeared, the kittens got very vocal and we were able to find one who was caught in a rat trap. Fortunately it was still alive and we were able to save it. I saw one other kitten, estimated at about 3 weeks old.
Since then, we haven't seen or heard mom or kittens. I think mom may have taken them elsewhere, but I am so afraid to close up the attic until I know for sure. Mom is probably too smart to fall for the cat trap again, but we set out some tuna outside the trap and it was never eaten.
Any advice? Is there some fool-poof way to bait a trap for a 3 week old kitten (without attracting other undesirable critters?) Help! This whole situation has me so stressed out.
Call your local rescue group for help and tips, they can either loan or rent you a safe have-a-heart trap to trap the momma cat and kittens. You should definately attempt to trap before you close off the attic. You could also try to place the trap at the entry where she was coming and going, and place enticing food in the trap. (such as tuna in spring water, NOT oil; or sardines, NOT the type in mustard sauce, cooked white chicken or even canned cat food). But, you MUST keep a vigilant eye on the trap (not only to monitor for a cat, but to keep the food inside fresh. Plus, if the weather is very hot or cold, or the atmosphere in the attic is too hot or cold, being trapped in a trap wouldn't be good.
Try sneaking up to the attic in early morning or late night hours, being very quiet and listening for mews, but try to avoid stepping in areas the kittens may be hiding near or under insulation; these are the times momma cat would most likely be either out and about searching for food, or bedding down with the kittens. If the kittens are LESS than 3 weeks old, they will be crying out for the momma to nurse up to 4 or so times a day. If the kittens are OVER 3 weeks of age, they might cry out to nurse only a couple or few times a day.
What type of insulation is in the attic? Is it fiberglass or foam or? Exposed fiberglass insulation, for example, isn't good for pets.
Are you certain momma cat is feral, or could she simply be a stray? How did she react when trapped, were you able to handle her?
Please, make all attempts to trap them all and keep them together. If they're still nursing, they need momma cat every few hours.
Please don't take them to a kill-shelter, call all rescue groups in your area and attempt to place with them.
Fortunately it was still alive and we were able to save it. 
I saw one other kitten, estimated at about 3 weeks old. 