Over the past few days I've noticed a number of instances in which a British person has referred to a child (whose sex is unknown) with the pronoun "it", as in the following:

The smaller child has its eyes closed, and the bigger one its eyes open. (celebrity "news" story, LINK. Actually referring to one boy and one girl, but the writer does not appear to know which is which)

each child has its moment of glory as it goes up to collect a certificate proving its status as a "Young Egyptologist" (Swansea University, LINK).

To me the singular pronoun "it" sounds very strange when used to refer to a human, especially in the latter case where "it" is used multiple times; my initial feeling is that the use of "it" implies nonhuman characteristics (the only regular use I can think of hearing is offensive disparaging reference to someone of ambiguous gender). Oddly I don't have any such problem with singular "they" which seems like perhaps a more common (US English) way to avoid the "he/she" dilemma.  Indeed, google search for this use (e.g. ..."child has its"...) seems to give an abundance of UK sites once other kinds of cases are discarded (like "Parenting any exceptional child has its challenges", or reference to "child" that is not human, such as node/hierarchical structures).

So it's probably just that "it" is more acceptable to refer to a child in UK English. A quick scan of some other options suggests that this may not be true of adults. For example, "person has its" doesn't seem to give the same kind of results (most of the "neutral references" tend to be from non-English-speaking countries, or referring to a legal "person" which may or may not be human).  Nor does "human", and interestingly "teenager" doesn't seem to do it either. So maybe this use of "it" is only OK before a child hits puberty. But it's OK to use "it" to refer to it before then.