Question

the child was given an injection convert into active

Answer 1

An injection was given to the child.

Answer 2

here is your answer
the child was given an injection
active voice=He gave an injection to the child.

( explanation: in active voice there must be a subject and an object in the sentence but here when we r given with this passive voice here the subject has been omitted so we will insert one subject of our own choice suitable to the sentence and i have chosen "he " as subject and rest is same when we r given with was given in passive so it will become gave in active as whenever we r given with 3rd form with a h.v in passive it changes into 2nd form in active without using any h.v ( helping verb))