Originally Posted by
pinniped
I would definitely carry the notarized letter. Whether you need it or not depends on the immigration officer(s) you encounter along the way, but I'd want to have it just in case.
Be aware that in the UK certainly, and probably other countries, not everyone will have heard of a notary. While they exist, they aren't a common thing here.
The letter signed by parents may still be useful, though, especially if it has a contact telephone number on it. Just don't expect anything other than "it's what?" if you point out that it's notarised.
Neil