Forty-two people were injured in Friday's shooting in two mosques in Christchurch, with the unidentified child and another person in critical condition, New Zealand Police Commissioner Mike Bush said in a statement.
The 4-year-old is taken to a children's hospital in Auckland.
A 28-year-old man, presumably Australian Brenton Tarrant, who allegedly filmed his ransacking at one of the mosques, will appear in front of the Christchurch District Court on Saturday for murder.
Two other unidentified persons are still in detention.
