You would only have a TFN if you are working and potentially paying tax. So generally anyone under 16 would not have one. Closest might be a Medicare Card whic

You would only have a TFN if you are working and potentially paying tax. So generally anyone under 16 would not have one. Closest might be a Medicare Card which gives you access to free/discounted public health that can be used as part of identification. Usually children are on their parents card. Drivers licence is also a primary identifier, and students can use their school student id.