If you want your grandchild to access the money you save when they turn 18, a JISA could be a good option. Grandparents can’t open a JISA for a child (unless they are their legal guardian) but they can pay into one.
Ask your grandchild’s parents if they’ve opened a JISA for them, and use this as an opportunity to agree on how much you can each contribute to the account to avoid going over the annual limit.
JISAs are also helpful when it comes to inheritance tax.
Grandparents can open a child savings account but the child may be able to take the money out whenever they want, depending on the account.