Sorry, I stand corrected. This is from the Foreign & Commonwealth web site:
Ensure your passport is valid for at least six months and in a presentable state. Holders of passports with just a short period of validity remaining or which are in poor condition have been refused entry to the Czech Republic. Children aged 15 and above must have their own passports. Those travelling on a parent's passport will be refused entry to the Czech Republic. You are also advised to carry with you a photocopy of the datapage of their passport at all times, for identification purposes.