Well I've always had dd's checked and we've flown in the uk with easyjet, BA and BMI. Because she's always had one, I've never been asked for any other type, but I'm pretty sure they do need some form of id. Maybe you should check with the airline you want to fly with.
Check the small print of whoever you're flying with. Easyjet only require photo ID for the adults children are travelling with. I discovered this earlier this year when ds1 and dds passports had expired. Went rushing to the website to check and sure enough it was fine. Might be an upper age limit though, so worth finding out now.