Then just refer to "the child." "They" is plural. While it might be suitable if the number is hypothetical, in this case it is clearly singular. "The child" is suitable and there is no sound reason to use the plural "they." This especially true today when "they" is being pushed as a non-binary pronoun. This political usage cannot be ignored.
It’s only political if you make it that way.
I was purely trying to explain the English language to you.
I give up.