Vivienne Pattison, a trustee at MediaWatch UK, was speaking after the report by AgeChecked also found more than a quarter (28%) of kids are using the internet before they reach school age.
It found many children are online before they learn to read to write, with 75% of parents saying they were concerned their child might be able to access pornography.
71% of parents asked were also worried that their children could access social media, and video sharing sites also ranked as a high worry (71%).
Explicit gaming sites and accessing restricted goods like knives and e-cigarettes were also a worry.
The AgeChecked study found:
75% worry children access pornography
71% worry children access social media
71% worry children access video-sharing
51% worry children access downloads
46% worry children access retail sites
40% worry children access restricted goods
Speaking to Premier Christian Radio Vivienne Pattison said: "Do exactly the same as good parenting in the offline world.
"It's a case of getting alongside your children and making sure the channels of communication are open, knowing what they're doing and just being aware.
"If all you do is worry without taking any action, it's not particularly productive, but there is help out there.
"You can make sure you set parental controls in the setting area of that device [computers, smartphones and tablets], so that they can't make purchases, and they can't suddently spend lots and lots of money.
"Just be a bit sensible and don't leave your accounts logged in so they can't click buttons and my-goodness-knows-what without knowing what they're doing."
Listen to Premier's Hannah Tooley speak to Vivienne Pattison here:
