Crawling as a pure definition means that the baby can get from point a to point b in any fashion but not on two legs. Which means it could be traditional fashion like on all fours, slithering forward or backward on tummy or even moving along in a sitting posture. If all other milestones are on track it is possible your baby may skip this and move directly to standing.

Probably your child could sense it may be hurtful for his knees. Keep him on a thick bedding on the ground and you start crawling they learn by seeing.

am so sorry.. I replied in different column

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https://en.m.wikipedia.org/wiki/TORCH_syndrome