I’ve been reading this Ask HN thread on Hacker News on the topic and thought of jotting down a TLDR in case someone finds it useful. Some of the points are in verbatim.

• Enable automatic updates and take away their admin privileges.
• Force them to only use pre-installed apps on the tablet/phone that you’ve selected. By pre-installed, I mean pre-installed by you.
• Install ad-blockers on all devices. Preferably something like uBlock Origin.
• Set up a Pi-hole and configure on their devices
• When buying devices for them always prefer iOS. iPads seem to be the general go-to choice of the HN community.
• Create desktop shortcuts for common tasks. Eg: if your dad checks news first thing in the day, create a desktop shortcut to that news site.
• Tell them to be suspicious of email links that require them to log in
• Talk to them about being conned / scammed. That’s by far the most likely way for them to get victimized online.
• Talk to them about real world analogs to pop-up ads that look like virus scanner alerts, talk to them about people pretending to be someone they know
• Get them to consider “what do I really know, and is this too good to be true”
• Make sure they know to call you if they get a virus / malware popup they think could be real
• Tell them about phone scams

While some of these expect you to be fairly technical (eg: setting up a Pi-hole), a majority of them do not.

Another point that wasn’t mentioned in the comments but I highly recommend – be kind and attentive when parents call you about technical issues. I used to be (or used to act) busy which led them to call me only on dire circumstances – something you would not want to happen.