I already have Codice Fiscale (You think you have or do not remember) but how to check it & IF it is valid?
I have already valid Codice Fiscale but lost my certificate
(or they say it is old and you need a new one).
You can apply for a new Codice Fiscale certifica the same way, no problem.
How longer Codice Fiscale and Codice Fiscale Certificate valid?
Your Codice Fiscale is valid for life. Certificate itself is valid usually at least 18 months.
How to apply for my underage children?
Only 1 parent is sufficient to sign the application for underage child(ren) BUT parent needs to have their Codice Fiscale certificate first and when applying you need to add your family certificate at least in english (if you do not have Italian version) to show that they are your child plus valid passport / id main page copies of both parties.