I find that giving momma cat some wet food daily *which she should get anyway) will help get the kids eating it alot sooner, they watch her and between 3 and 4 weeks will start checking out what she is eating, and try it themselves.
Then you can offer a bigger dish so they will get right in there, walk in it, etc and once they are eatting well enough that they really only nurse for comfort they can be completely weaned.
At this point they must be pulled/seperated completely from mom or they will continue to nurse, and she needs a couple weeks to dry up so she can be spayed
I have never found it necessary to do anything to wean the kittens I have fostered, nor did my friend have to wean her pedigree BSH kittens. In both cases we fed the mum in dishes put where the kittens could find them, and given that kittens like all young animals explore by eating, and kittens copy what mum does, one thing leads to another.
Do give them a good variety of food. I gave mostly commercial kitten food but also gave treats of raw mince and cooked white fish (not at the same time!)
In essence look after mum - feed her as much good-quality food as she wants to eat, and she will look after the kittens.