The excuse of the NW"T" translators is that the word "paidion" - child - is neuter and any pronouns associated with it are necessarily also neuter. Thus at Matt 18:2 the text says that Jesus stood the "little boy" [KIT] - "paidion" - in their midst and said to "it" [Greek "auto"].
The problem is of course, that the pronoun is not establishing a cultural medium from whence children are addressed, but is simply following grammatical rules that are detirmened by Greek syntax. The English translator is not bound by grammatical restrictions of Greek syntax but must convey what is said into readable English.
The rule is that while children in the womb may still be referred to as an "it", when they are born and are living an independent existence they establish their own gender values. The conventional idiom is that if no gender is mentioned, to use "he", but some prefer to retain the expression "child" to translate the word "auto".
Having said that, however, there is a curious inconsistency when referring to Jesus. At Lu 2:27, the use of "auto" causes the NW"T" translators to refer to Jesus as an "it", but a little farther along, in verse 40, the same word "auto" is ignored and Jesus suddenly has gender! He is dutifully referred to as "him".