You set up a timelock with nLocktime at a future block around the time you will turn 70. But if you suffer a heart attack and die at 60, your children will have to wait 10 years to get access to the coins.
There are easy ways around this, as I briefly explained here:
https://bitcointalk.org/index.php?topic=5394317.msg59853530#msg59853530. To elaborate:
The first scenario would involve me keeping the timelocked transactions secret, such as locked in a safe in my house or a safe deposit box at a bank. My family know about where they are stored, but would only be able to access them after I die. For added security they could be encrypted with a key only my family know. I create and sign a timelocked transaction, locked 1 year (for example) in the future, and hide it in my safe. If I am still alive in 11 months, then I create and sign a new timelocked transaction a year in the future from now, destroy the old one, and and replace it with the new one. Repeat every year and your family will never have to wait more than a year to claim your coins (or whatever time frame you choose). If you wanted you could even make up decades worth of timelocked transactions in advance, with a new one unlocking every month (for example), and just destroy them one by one as time goes on.
The second scenario would involve me sharing the timelocked transactions with my family as soon as I sign them. Again, 11 months in the future, I move a single input from the timelocked transaction, thereby invalidating the entire transaction (I could even keep a single input of a few thousand sats which I repeatedly use only for this purpose), and then create and sign a new one and hand it over to my family.