A PAN Number is a good idea if the Minor has a source of income. While it's not required, it is a requirement for anyone who has a source to earn.
You can submit a "Change Request Form" when a Minor turns 18. The PAN number will remain the same but the adult PAN Card will include a photo.
You can correct your PAN Card by filling out a 'PAN Request Form' on the official website of NSDL and UTI Technology Services Limited. They are authorized to do so.
Any type of PAN Card change requires that you provide the required documents as per the change request form.
Click the link to download the PAN Card Request for Change.
NSDL PAN Service