What Delays Can I Expect from a Child That Has Down's?

My youngest daughter who is 9 months old has down syndrome. I guess I just want to know what kind of delays to expect from her and if there is anything I can do to help her. At this point she is behind as far as sitting up on her own, she's not crawling, or pulling herself up. I think alot of this has to do with her low muscle tone. I want to get an idea of what to expect from her mentally and if there is anything i can do to help her though the years.