I need to get my kittens to stop suckling

Okay so my kittens are almost 3 months old (they were born on 17th of January 2025) and they haven't stopped feeding of their mother yet. Were getting kitten food but I don't know why they are still suckling and I'm scared for the mother because she's been a lot more tired and hungry recently. I'm thinking that her kittens since there supposed to stop suckling by now she's ran out of milk and she's eating to try and keep the milk for her kittens (she a first time mother.) And she's also been walking away when her kittens are mid suckling. (For the boy one call him Smoosh and the white one Vanilla)