My cats are around 10 weeks old should they be still nuresing?

They should be be weaned by now, but momma knows best. Hopefully you are offering them kitten chow. I am not trying to be nasty, but there are so many reasons to get a cat spayed/neutered, please consider it.

Bushg is right. Offer the kittens some kitten food. Mom Cat will eventually push them away. And please get her spayed. There are millions of unwanted cats and kittens abandoned and homeless all over the world, and especially in the U.S.

(Bushg, clean out your mailbox!! )

A kitten should stay with its mom for a mininum of 8 weeks and preferably 12 weeks, But they can be weaned at 8 weeks, although they'll continue to nurse if mama lets them.
Kittens need twice the amount of nutrients as a adult cat, but can't eat nearly as much, so you should get them a "good brand" of kitten food that has extra protein, fat, vitamins and minerals. This will give them the healthy start they need for good health!