Mother cat eating her kittens' food

Why is our cat eating her kittens' food?
   
We have bowls in separate locations for our cat and her 4 1/2 week old kittens; however, the mother cat ignores her own food and finishes all the kittens' food. Both mother and babies are being given the exact same kitten food (a constant supply of both hard and wet food) the only difference is the bowl we put it in.
   
It's a problem, because I don't know how to get the kittens to start the weaning process if the mother won't let them get to the food. Moreover, she's become finicky and won't finish the food in her own bowl and begs for more, even though she's devouring the food from the kittens' bowl.
   
Please help -- we didn't know the mother was pregnant when we adopted her from the shelter, so the litter was a complete surprise! I've never raised kittens before, and any advice is extremely welcome!!!

It's pretty hard to understand why the cat prefers the kids' dish, she can't tell us. Maybe she likes the color, or shape, or how high the sides are. Cat's like low-sided dishes, so they can crouch down & still eat comfortably.
   
A couple of solutions:
   
1) Put the kittens' dish in a box with a tiny kitten-sized door (enlarging it as the kittens grow) & some 3" square windows in it for light - cut the holes out with an old serrated steak knife, the best tool for cutting cardboard. That way, she's stuck with her dish.
   
2) Put the kittens in front of the other dish & let them use that.
   
3) Get a duplicate dish so they both look the same.
   
4) Change out all dishes to a pair that matches, maybe a wider model with low sides.
   
As to the "finicky", I think she's just jerking your chain. Tell her in no uncertain terms that if she wants anything else, she can go use the other dish. She's getting more calories than she needs, anyway, so if she pouts & doesn't eat a couple of afternoons, fine, she won't get any fatter. She'll eat when she's really hungry.
   
I think she should be getting a good adult food rather than kitten food; she really doesn't need the calorie level of kitten food. Telephone your vet (leave a message & have them call you back, I've never known a vet to charge for a phone question) & ask what cat food she should have. Her body's not supporting babies anymore, & she's not nursing as much, so she doesn't need so much extra.
   
The kittens can be adopted out by 8 or 9 weeks. If they're particularly small, hold them until 9 weeks to give them a chance to fill out a bit. Find out if your vet has an "adoption pen" in their office; many do - & ask if your kittens can be checked into the pen during office hours.
   
For homes, you can ask around at work, with your friends, your kids' friends & families, the neighbors, & any clubs you belong to. You can also contact any private adoption groups in your area for advice on placing the kittens.

FYI,
   
As long as mom is nursing, she should be eating kitten food anyway. This will help her feed her kitties better. Just call your vet and ask.