I got the majority of mine at 1 week and for the first few days they all had diarrhea and a couple slept A LOT. They all survived, thrived and are doing great at almost 3 mos. I was pretty dang nervous though!
A friend of mine got 3 Buff Orp chicks at the feed store that she was going to keep for a few days and then give me to raise and. Weeeeell, she didn't provide a lightbulb over them as I instructed and even kept them in the coldest room in her house, and you guessed it, first one died then another. So she brought the survivor over, and I gave it sugar water from a medicine dropper every 30 minutes and carried it around all afternoon in my pocket. That night I got two similarly aged Rhode Island friends to brood with it and they did great together. It is a fine healthy pullet now. So, not that you want to have a pocket pet, but it could be worth a try if it is getting picked on and having a hard time pulling through. Good luck!
I love that shiny marble in the feed suggestion, I'll have to remember that one!