we gave our godaughter a thin silver bangle for when she's grown up, and a book with all the beatrix potter stories in it. you could omit the silver bangle if you're not a godparent.
There's a really nice jeweller called Kit Heath who does a lovely children's range. Based in Covent Garden but you can order over the phone, and they'll post out to you.
www.kitheathjewellery.co.uk