I obtained my daughter's first children passport when she was just a few months old. Now she is three and during our last flight an immigration officer complained that her passport had a baby photo. He let us through but it sounded like he was making an exception and he strongly advised us to renew her passport ASAP. However, it does not officially expire for another few years until she's six and it should have been obvious at issue that her appearance will drastically change.
Obviously a new passport costs money and effort so we'd prefer to just keep using hers as long as possible but could we get into trouble for doing so and in the worst case be declined entry? Are there certain countries where this would be a bigger problem than others?
By the way, if that's relevant my daughter holds a German passport and oddly enough the immigration officer that complained was also a German one.