Lifetime ISA - cash or stocks & shares?

[breadmilkandchocolate]

I have decision paralysis, so looking for a steer!

I want to put £4k into a LISA for my 18yo son, and plan to gift a further £4k a year until he is ready to buy his first home. Obviously we don't know when that will be but he's showing signs of being a high earner who will want to settle down early, so best guess is 5-10 years (with deposit potentially topped up by an inheritence). We need to decide between a cash LISA and a S&S LISA. The cash interest rates are rubbish, so S&S are tempting, but the risk of a market turbulence seems high for something as critical as your first home - paying months of additional rent while waiting for a downturn to reverse itself could more than wipe out any growth. Thoughts?

I'm too risk averse to go for a S&S one. I can't afford to lose anything! Also, we'd be using ours within 10 years (more like 6) of opening it, so cash is safer in the short term as S&S could dip right before we need it. 10+ years I'd expect S&S to have smoothed out and increased over all despite dips.

DCs child trust funds are S&S and the difference between DS1 and DS2's set up a year apart is stark as one was closer to the 2008 crash and so lost a lot early on.

lifetime Isa because he will get 1k a year in government bonus payments

They're both lifetime isas, so will both qualify for the extra £1k. Only question is whether the pot is held as cash or invested in s&s.