One thing that is that while a child has the full tax allowance (so is unlikely to pay tax on savings interest), interest on money gifted by the parents above £100 per annum is taxed as though it is the parents. With that in mind, it may be worth opening two accounts - one for money gifted by parents, and one for grandparents/everyone else. This helps to demonstrate where the money originates.
If you're looking to make regular payments into the account, it's probably also worth considering that most savings accounts will lose money in real terms. If you're investing over 18 years, then it's probably worth considering equities - through a JISA or some other means.