Baby rabbits need to be with their mothers until they are at least eight weeks old, so these bunnies are definitely being sold too young. I would report the seller to the proper authorities, as in many places it is illegal to sell rabbits under eight weeks.

Where I live there are some pet shops who sells really young rabbits, I think around 4-5 weeks old.

To my knowledge they do need milk in this age – they can survive without, but most of the time they couldn’t get a good imune system, so they will be more ill than other rabbits. Mostly they stay smaller than other rabbits too.

Rabbit babies need milk for their immune system until they are 6 weeks old, I think. Many breeders in Germany sale their baby rabbits with 6 weeks.

But they should be with their mum to get a good social behavior towards other rabbits like at least 8 weeks. And they do get a better immune system if they have more time to drink milk.

Some let the rabbits stay with their mum until they are 10 – 12 weeks old, because then they have more time to learn from their mother
(But you have to pay attention to the bucks, as some dwarf bucks get sexually mature around 12 weeks.)

I think that at that age, they should still be eating their mother’s cecals.

Manic is right, it’s mums cecals they need the most after 4 weeks till they start producing their own at 6-8 weeks.. It helps build up the healthy gut flora… The best thing would be a probiotic supplement from the vet.