any ideas of ways in which to finance a loan for my sons next house purchase

Property Investment

Hello colleagues.
Looking for options/suggestions re finance for my [LL] son next house purchase. He would live in the property, then turn it over to the rental market. This is his business model.
He suggested I 'loan' him £100k..recouped through a 'Charge' being placed on the property when he sells in 10 years time. Has anyone tried that avenue?

It can be formally, or informally done, to ensure transparency with his other siblings.
Its been suggested that a witnessed/dated 'position paper' detailing this scheme & the payback to my estate when I die, would suffice when the whole family supports the idea. And may want to follow suit!
Mmmmmm...both food for thought.
Thank you in advance.