Can you pay into another adult's savings account?

[busymyfoot]

My inlaws want to start gifting some money to my children, age 19 and 17, on an adhoc basis. I don't know how much or how often, but they want it to be saved towards a future house deposit. I know they could gift into my 17yo's Junior ISA, but only until he turns 18. My understanding is that after that they would have to gift it to their current accounts and rely on them moving it somewhere sensible. Is that right? Or are there adult savings accounts (with decent rates) that can be gifted to directly?

Ideally I want to find accounts that don't have restrictions on how much can be paid in, or how often.

(To avoid drip-feeding, DC19 already has a LISA and an adult ISA, which I contribute to occasionally by transferring to his current account and then helping/encouraging him to move it, so I'd prefer not to have to do the same for the grandparents' contributions, if possible).

Savings accounts, isas ect have account numbers the same as any other. Of course you can send payments directly to it.

You can definitely pay into a LISA, we do it every month. I'm sure you could pay into any account - think about when you owe someone some money, they just give you the account details & you transfer it. This is no different, surely?

It's no different to transferring into their current account, you just need the Acc number and sort code of the savings account instead.

I should have also said that the existing ISAs are S&S Isas with Vanguard. They allow gifting into child ISAs but I can't see an option for gifting to the adult ISA. That's presumably because they have an annual upper limit which might be unintentionally exceeded by third party gifts.