Like every other investment such as real estate, stocks and other forms of investment we know that you can invest in that kind of things and then you get something like say a Certificate or a Binding Document as a proof that you are part of that investment, now that of bitcoin all you have is just your address, your password, key and seeds as proof of the ownership of the wallet.
BTCSo now if one is considering buying bitcoins and saving for his/her children in the future is there any way to do that with bitcoins apart from having to write down your details somewhere. I'm asking because with that kind of stuff if no one knows your seeds or password no one can get the coins.

I don't have a child yet, but I am saving a quarter of each profit I got and put it into another wallet where I wrote the password username and email address and email's password onto back of my portrait picture with a note "Your fortune is here" and I told to my mom in case I die without having a child or I died first. Yeah I know it is kinda weird and very futuristic but I am just making sure I won't regret things if I end up with no money in my pocket and leaving my family/child helpless and no foods in his stomach.