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.

because kids are kids, you may want to do this with a hardware wallet. the updates will ensure that the kids will be able to spends the coins at some distant point in the future, even if there is a major change in the protocol (for example, the way public addresses are formatted). this wont be quite so easy to lose or destroy as a paper wallet as well, and wont be subject to breach simply if someone finds it (the damnable paper wallet).
most paper wallets have this terrible flaw; the private and public keys are clearly labeled and visible once you obtain the document. the best paper wallets have your information on them, but in way that only you understand. if its too clear and someone finds the paper key, then you just gave away the keys to your kingdom in a very clear and concise format