Mobile phone tarrifs for the kids - anyone know any good offers?

[Nixz]

I want to get DD a mobile phone but obviously dont want her to be able to run up huge bills!
Does anyone know of any good tarrifs? She has a pay as you go tarrif now but there have been times when she hasnt had any credit and hasnt been able to call me.
I feel better with her having a phone, it has been very useful at times!
I have searched a few of the mobile networks but was wondering if there were any 'less known' networks that somebody has used.
Thanks ladies

on o2 online pay and go if you top up £10 a month you get 300 free anyone/anytime texts and 500 mins to another nominated o2 phone, and you still get to use the £10 however you like. dp works away all week every week and we both use this tariff as it's cheaper than any contract and keeps the landline bills down

I am with Tmobile and her Dad is with orange so that tariff would probably not be as cheap for us!