反对!

绝对没有必要. 小孩的骨头和大人的不太一样. babies have more bones than adults plus babies' bones are much smaller. as they grow up, some of the bones will fuse together. Some of a baby's bones are made entirely of a special material called cartilage. Other bones in a baby are partly made of cartilage. This cartilage is soft and flexible. During childhood, as you are growing, the cartilage grows and is slowly replaced by bone, with help from calcium.

So babies don't need any protection on their knees when they are crawling.