Days old chick with 2 and 3 week old chicks?

I've been wanting to add a Buff Orpington chick to the group but..I have two chicks that are two weeks old and two more chicks that are three weeks old...would it be alright to put the days old chick with them in the same brooder or would they hurt her?

I wouldn't recommend it. There's a significant size difference and the day old could end up crushed in times of excitement when they run and jump around like little bugs. Unfortunately I figured this out myself through experience. 1 week apart is the most I'll do myself now.

You are dealing with living animals, no one can give you any guarantees one way or another. Sometimes you can mix them just fine. Other times the younger chicks are injured or killed. With living animals you just can’t tell what will happen. I had a two week old chick kill its hatch-mate, no age difference. Does that happen a lot? No, but it can possibly happen. The more age difference the more likely to happen and the more likely it is to be serious.

If you really want to try you can. It might work. But I’d try it when I could monitor it and have a plan B ready. Maybe make an open-topped box out of hardware cloth big enough to cover the chick and have food and water inside if you turn the box over on it to separate it from the other chicks. And I’d suggest getting at least two so it has a playmate. It can get pretty lonely if it can’t cuddle with another chick.

Ridge beat me to it, suggesting you get two day-old chicks, not just one, and not just because it needs a friend.

When adding new chickens of any age, a single one gets all the focus and attention, while with two, the attention is diffused over the two of them. In addition, Buffs are very docile breed and a single would have a difficult time gaining self confidence. With two, they will give each other the confidence they need to cope.

The two and three week age difference isn't insurmountable. But you do need to partition off the new ones until they grow a bit. Have the brooder in proximity to the older ones so everyone knows they're part of the same flock. If you haven't already put the two older groups together, start doing it immediately. The sooner they all become a flock, the better.

After they've all been in proximity for a week, try putting them all together. Referee, but give them a chance to establish a pecking order. Step in if you see a single chick getting mobbed by several bigger ones at once. In a few minutes, they should have things worked out. If not, use your position as "flock leader" to discipline any trouble makers by poking them on the back each time they cause trouble. This is how chickens do things when younger ones step out of line.

The ages are still so close, you should have no trouble pulling this off.

Thank you SO much everyone for your help! I really appreciate it!

One more thing that I'd recommend would be partitioning off a section of the brooder for the first day or two, at least. When we mixed a day old blue Cochin chick, Sesame, and our six week old brahma, Calliopeep (Callie), we separated them at first and then introduced them by keeping Sesame in our laps where Callie couldn't peck her and letting Callie walk around her. They were totally fine with each other, and now spend all their time together; the size difference is adorable! Now, they were both single chicks, and I know this won't always work. I just wanted to point out that it can be done, and if you make it clear to the older chicks that you are protecting the little peep, then they'll be a bit more likely to leave her alone (in my experience )