Hello,
The account you need is a "gift savings account" (also called a "gift account"). Gift savings accounts generally deliver the same interest as youth savings accounts. The difference between this type of account and a youth account is that the child does not manage the account themself. But the money in the account still belongs to the child.
To find the banks which offers the best interest rates, just compare youth savings accounts and then ask the best-performing banks if they also offer gift savings accounts.
Investment accounts bear more risk, because they can incur losses. The fees charged are also noteworthy. You should only open a flexible investment account if you have a reasonable tolerance for risk and expect the money to remain in the account over a long term (rule of thumb: at least 10 years).
You can find more information here:
Youth bank accounts in Switzerland
Savings account and youth savings account comparison