Weaning is a natural process. It is not taking a kitten away before it is ready! Just make moist food available to your babies, either canned food or moisten the dry kitten food. Kitten food is good for the Mom, too, because she needs the extra calories. Some kittens are eating solid foods by 6 or 7 weeks, others just won't touch it! But as they grow, they all eventually eat the solid food and quit nursing. (Except Kluchetta's crazy baby-5 months
? That is one patient Momma! LOL!)
I foster kittens, and they always stay with their Mom for 8-10 weeks, and even if Mom leaves to be spayed and adopted out, the babies stay together! And if we end up with only one kitten, even if it is over 12 weeks, we do our best to put it in another foster home so it has other kittens to play with.
You can have people "pre-adopt" your kittens at 8 weeks, but let them know they will be little monsters unless they can stay with Mom for a few more weeks. Even if they are not purebred cats, often we suggest you charge enough to cover their initial shots and a little extra to go towards spaying the Mom cat.