Kids Passports - Get this sorted out early and check the usual turn around times for processing passport applications.
Also check who is eligible to witness your child's photographs (it must not be a family member) and the criteria the photograph itself must satisfy. These criteria are quite stringent see kids passport requirements.
However, as anyone knows who has tried, it is difficult to get the perfect photograph of a young child, as they do tend to move!
It seems that there is usually some flexibility when taking a passport photo of a baby or young child.
However, quite what is the extent of that flexibility does not appear to be officially stated anywhere in writing, so don't bank on this, and get your application and photos in early in case you need to repeat any part of the process.