It's a good thing not to be too young, since the idea is that if anything, godforbid, should happen to the child's parents, you as a god parent are supposed to step in and bring the child up. I suppose in real life it doesn't always turn out that way, but that is 'the big idea.'
i dont think its as serious as bring the child up................ i asked my local perv err i mean vicar this and he said " you promise to bring the child the knowledge of god"
go for a blessing and not a christening. the wording of the service isnt based around religious instructions and the god parents are called something like 'guardians'. your mum will still get to wear a hat to the church and its a buffet down the pub after.