Q: Should I be concerned about my baby girl's development? She is slightly over 7 months and does not roll over or move around much. She has little to no interest in tummy time and complains bitterly when on her tummy. She sits and plays with both hands free when you sit her up, but still falls over after a while. Please advise.
A: Every child grows and develops according to her own unique timetable. One area of development may normally lag behind others. Physical developmental landmarks are only one area. Language, social and cognitive milestones are equally as important.
Landmarks do not need to appear in any particular order. Some children can stand holding on for months before they are able to sit unaided. Furthermore, there's a big difference between being unable to do something like roll over and being able ... but not wanting to. One can be a sign of developmental delay, while the other may simply be due to the child's emerging individuality. The fact that your child doesn't like tummy time may mean nothing more than she doesn't like to be on her tummy.
By 7 months children generally roll over from both front and back, sit with hand support, reach with one hand, and transfer objects from hand to hand. They respond to their name and make sounds in response to sounds, enjoy social play and looking at themselves in a mirror, and work to get objects out of reach.
If a child is too stiff or too floppy, if she doesn't rollover by 5 months, sit with help by 6 months, or actively reach for objects, bear some weight on her legs, and try to attract attention though actions by 7 months, let your pediatrician know. This doesn't necessarily mean that she has a problem, but it would be wise to more closely monitor her development.
Milestones are discussed in more detail in the AAP publication "Caring for Your Baby and Young Child - Birth to Age 5".