I tried really hard to not have my kids stay in any one position longer than half an hour excepting when asleep of course. I moved them from, swing, tummy, bumbo, bouncy, jumper, excersaucer, high chair, floor on back, lap, then repeat.... I tried to make tummy time before a bottle so the tummy was empty & reduced spit up or reflux. I truly think this rotation helped my kids to develop muscles neccesary for upward mobility, since my daughter walking by 8 months & my son 9. My daughter was 10 months old when she climbed onto our dining room table!! I would think possible genetic thing, but my daughter is adopted, so has to be environmental, i would think. Hope this helps....Oh also, if you put her on her tummy, but with a little pillow or folded towel under her top half, kinda making a wedge with her head up a bit, this will help prolong the session. best of luck.