Giffgaff being pay as you go many parents will see that asa great option for their kids. However most kids, even at a young age, will know more about the technology than their parents but they won't be as knowledgeable about child protection as their parents, especially online. Browsing te O2 website just now and reading their parents page and it has a lot of good information for parents on general child protection, what O2 do and what O2 can't do to protect children using mobile phones and the internet. It's a great summary of O2s responsibilities and a parents responsibilities as well as a source of guidance on the O2 features specific to child protection.
I'd like to see a similar parents guide on giffgaff. At a guess I'd say that giffgaff as a cheap pay as you go network would be more appealing to parents than a 24 month contract with O2.
Ideally it should be prominently featured on the website, perhaps under the help tab. I've also seen similar parents guides made available as a downloadable .pdf which is a great addition to a browsable guide as above.