The more time babies spend on their tummies, the earlier they might begin to roll over, crawl on their stomachs, crawl on all fours and sit without support. Start by laying your newborn on his or her tummy across your lap two or three times a day for a few minutes. As your baby grows stronger, place him or her on a blanket on the floor after a diaper change or nap. Arrange age-appropriate toys within his or her reach.