I also recently asked this question and I got a lot of different answers. The majority seemed to think that your chicks would do just fine since they are all really young and very close in age. I added one day-old chick to a group of 12 week old chicks and nothing happend.....everyone was fine. Some people suggested that I separate them with some chicken wire, but keep them in the same area so that they could see each other but not "get at each other". I think that is only needed for older flocks. Trust your instincts and keep a close eye on the babies, you will know if you need to separate them if they aren't allowed to get to food or water by the older ones or if they are picked on. I don't think that they start to develop a peck order until about 3-5 weeks. I bet they will be just fine.