Looking for advice...?

Normally I don't do this but it's better to ask then not. My fiance and I were recently awarded temporary custody of her 9 month old nephew. It's for a year until the parents can prove to CPS that they're deserve a second chance. By all accounts, the child looks like a fairly healthy baby but I along with my fiance can tell that he's behind developmentally. He's been kept in his crib and car seat most of his time as a child and barely rolls over, can't sit up or stand if he holds himself against anything. When he does roll over, he can barely hold his head up, attempts to scoot forward but doesn't go anywhere and never reaches for anything...just gets up close and looks at the object of interest. I've done a little bit of research in to how far along he should be at this stage in his life and all any of the articles suggest that I see a pediatrician immediately. I'm looking for a little guidance if anyone has seen or dealt with a problem similar to this or if anyone can point me to some better research sites for answers. Also, if anyone has any suggestions or articles that can assist me in helping him develop his skills and get caught up. Thank you.