You should definitely start introducing all healthy foods to your chicks at this time.
Chicks can begin to crack millet at about three weeks old.
It is important to introduce a good variety of healthy foods to your babies.
A hungry baby will not want to try a new food but once it's had it's fill of its regular food, it will be more than willing to try pellets, a wide variety of vegetables and hard boiled eggs. The larger variety of foods you offer, the quicker the babies will wean and learn to eat on their own.
Like anything thing else, you can't expect immediate success so work with the babies on a regular and consistent basis offering a good variety and soon you'll have healthy and happy chicks!