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.

BTC

So 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.

Actually it is a great plan that the other family should do. Investing in a bitcoin for the future of their children is the wisest thing since they are assured that all their hardwork woll be paid-off; 
In bitcoin all things can be achieve with them so their child can be successful and financial stable in future.