Help! Underweight chick!

[Goldsfam743]

We have 6 chicks barnyard mixes mostly barred rock and Easter eggers. One little chick, Tiana(green), is feathering it faster than the others but she's much smaller! She's just as active, eats, drinks, poops fine. I weighed them today. They blue (Cinderella) and red (Mulan) were the smallest at first and have the least real feathers.
We were told they hatched on July 4th. So they're almost 3 weeks old.
What can I do to help her??

 

[FluffyButtBabies]

At this age, gaining weight isn't really going to happen. Looks at their behavior. Do they act normal? Everybody eating and drinking well, with good poops? If they weigh less and are smaller, but don't visually look skinny or sickly, then don't worry too much about it. Some chicks just grow more slowly than others, or are runts. They can still be happy and healthy. Make sure they are getting all the proper nutrients in their feed, and that they are eating it consistently. I have a batch of four chicks that all hatched on July 4th as well. But despite acting the same and eating well, they are all different sizes. One chick is significantly larger than the others, and one is so tiny you wouldn't have even guessed they were the same age. But all of them are healthy and they are all growing (just at different rates)!