Please know I don't want to be an alarmist, but my cousin and his wife had 2 boys who had certain development problems that were not of any concern to their pediatrician at all.
They had to take the oldest to be tested for Kindergarten readiness and the pediatrician on staff there took one look and suspected Muscular Distrophy imeadiately. They were referred for further testing and found both little boys had Duchens Muscular Distrophy which is passed on by the mother being the carrier. This affects mostly boys, but there are many types of muscle affecting diseases.
If a toddeler isn't crawling and not getting around by another way I'd be very concerned. Some who don't crawl, roll or scoot on their butts or something to get around. I would seek out a childrens hospital or a pediatric neurologist and don't waste precious time.
You're in my prayers and good luck.