Petra is a long hot walk on stone with animals, unfenced drops and no shortcuts — very good from about eight upwards and hard work below that.
Do the distance sums first
The Siq is over a kilometre before you see anything, the Treasury to the basin is a couple more each way, and the Monastery adds several hundred rock-cut steps. Fix a turn-back point at breakfast, not at two in the afternoon.
Petra Kitchen as the evening off
The operator runs the class for groups and families at all skill levels: five or more dishes made and then eaten, indoors, on Tourism Street. It works well as the thing you do on the evening of a long walking day.
Horses, donkeys and carriages
You will be offered a ride every few minutes from the gate onwards. Some are ticketed and most are tipped, animal condition varies a lot, and it is a much easier decision made before you are standing there with a tired child.
Shade and water are the day's real limits
There is almost none of the first past the Siq. Bedouin stalls along the colonnaded street and up at the Monastery sell water and tea at site prices, so carry more than feels sensible and top up whenever you pass one.
The long trails are not family walks
Petra to Wadi Rum on the Jordan Trail is 91.6km over five days with 2,354m of ascent and the trail's longest waterless stretch. With children the answer is a guided day out of Wadi Musa, not a section hike.