I have three that started with me at around the same period of time and are all within a month of each other. At 12 months one was walking confidently, the other was crawling and cruising, and the third was like you described...no crawling, no cruising, no leg strength, no self feeding, only eating purees and bottles and would basically hang like a sack when I picked him up. He is now 17 months and still isn't walking, but he's getting close and he is now feeding himself with no problem and eating the same foods as everyone else, drinking from a cup, and finally starting to interact more with the other kids and get more social. Still, when people see him they say "Aww, how old is the little guy?" and are shocked when I tell them...he seems more like a 12 month old than a 17 month old. However, he is sweet, happy and healthy and I think this is just normal for him. He progressed a lot once he started full-time with me as I rarely carry him and he has to be down on the floor with the other kids. Practice practice practice is what they need, but also some of it is genetic, so there is only so much you can do.