I wonder if these sentences are correct: "This is my child. It is its room" I'll be grateful for an explanation.
The rules are the same whether you are talking about a child or an adult. It is rude to call anyone it unless it is really impossible to know the gender - for example enquiring 'Is it a boy or a girl?' or 'Who was it?' when someone answered the phone and you don't know who they were talking to.
Hi guys,

Wih regard to using 'it' for a baby, yes, there are considerations of politeness. There are also considerations of 'distance'.

A doctor, for example, might refer in his notes to the child as 'it', because he is being clinical and has no emotional attachment or investment. Or I might say 'There was a small child on the bus and it threw up on my suit'.

Best wishes, Clive
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This is my child. -- fine

It is its room -- very odd; parents should know their child's sex. Much better would be This is his/her room.

PS: I now see that your question is in your subject line. Yes, a child can be referred to as it, for a brief time, before one is told its name. Then it is best to call it him or her to avoid antagonizing the parents.
Yes it would be very very very strange if the parents do not know whether their baby is a boy or a girl.

However, as having been discussed in another tread it is perfectly alright to use the referent it in a few situations, as in this one;

Is it a boy or a girl? of course asked just after the mother has given birth.

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