If a child is very weak after a disease or is physically weak in general do the following. 

Take a little bit of olive oil the do a dam (blow) on it after reading the following

11 times Darood/Salavat

1900 times “Ya Jabbar-o”…(Allah’s name)

11 times Darood/Salavat

Then massage the child’s body with that oil. Do this everyday for 7 days non stop. You have to do a dam (blow) on new oil everyday.

Inshallah the child will become healthy and physically strong.