my 10 mnth baby started crawling but his knee becoming black day by day bcoz of crawling .what to do

A. That is common to be seen so you should make your child wear lowers right now anyways the weather is little cold because of excessive rain so use that and in the area is becoming black apply some potato juice onto that leave it overnight and wash in the morning slowly the blackness from that area is going to be removed but you just have to practise this regularly