Baby Meatball

This is Meatball, three weeks old and less than half the size of the others. She isn't getting bullied and is usually out and about with everyone. She gets nervous when the bigger ones are really active because she gets bowled over. I've started taking her out in the morning to give her some vitamins in water and egg yolk to hopefully help her along a bit more. Any tips on getting a runt to thrive?

The others are getting so big they should be ready to go out in a couple of weeks, if she's still too small would it be better to buy a new baby to stay with her or keep one or all of them inside until she is?

She's so sweet. No matter what happens I'll do my best to keep her healthy and happy. They're my first chicks so it's been a fun and chaotic learning experience.