I recommend once again the excellent website from The Motley Fool .
They have a special Saving for Children section, and a Investing for Children discussion board.
FWIW I put the kids money, plus odds and ends, into a Nationwide kids account (not currently the market leader, but one of the most consistently high rates). When it gets to £1000 I take it out and put it into an M&G UK index tracker, which is unexciting but as safe as equities get. Low fees, too.
I'm putting the CTF money for dd2 (when it arrives!) into the F&C fund, but won't be adding my own contributions, as would rather invest them separately. (Cynical about what govt. might do with CTF funds in the future).
Are you coming to the City lunch on Thursday, lisalisa?