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.

It is a good idea and worth buying down now for one's children. By the time it becomes globally accepted, one's children are also relevant. Also, one can have it in reputable Investments too, so as Bitcoin is increasing in vallue, so also with the investment. As real estates and other like investment is applicable today, so will the bitcoin investment/invest will be releven