I took my boys up when they were about 6 onwards.
I would recommend having somebody else in the plane, to deal with situations that may arise - for the first flight or two anyway. And see how it goes.
The issue I had was that my ex demanded a 2nd pilot, which made fly-away expensive (I had to pay for an extra hotel room, food, etc). It was nearly 10 years before she gave up on that. (She had no legal ability to require this, BTW, but I gather it is not an uncommon controlling ploy).
My older son lost interest by the time he was 10 (7 years ago) but the younger one (now 14) became aeroplane crazy. He flies to a mid-PPL standard now, and could certainly land if he had to.
Headsets are obviously vital. The cockpit is normally far too noisy without headsets. My bose-x ones were fine - they have soft earcups. Some of the cheapo ones I have worn in the distant past were truly crap - like having one's head in a vice and would not be good for a child.
And make sure you have some juice in the tanks
And don't do anything stupid. A Seneca which lived in the same hangar as my plane got embedded in the side of a mountain, in a +TSRA, on a "VFR" flight on solid IMC. Killed 2 adults and a 7 year old. I doubt the pilot ever checked the enroute weather.