Your pet rabbits are mammals, which means that their mothers will provide them with milk containing all that they need to grow and thrive. That is, until they are about seven weeks old - at this point, she’ll stop suckling them and they will transition onto solid foods. This can be quite a tricky process, and during this time it’s best to be careful and not too adventurous with your young rabbits’ diets.
It's wise to be very careful when introducing new foods to rabbits - especially young ones
Once baby rabbits are about three weeks old, they may try to eat tiny amounts of the pellet feed their mother eats. By the time they have been weaned, this, alongside hay, should be all that they are eating. Introducing fresh food should be done very gradually, and with small amounts at first. Many people recommend that you don’t start introducing fresh foods to a baby rabbit's diet until they are at least three months old.