It's normal

Mostly its normal. But sometimes it may be due to hypocalcemia. Don't make the child stand even with support

Hello. 3 months old baby cannot bear weight on legs ...if we make them stand it's obvious that the legs will shake. Even the head and neck control will be achieved at 5 months of age. So nothing to worry about and it's just that first of all head and neck control followed by sitting and then standing. So don't make them sit / stand now till proper neck holding is achieved.