Hi there
This sounds like a wind-up

The Inca Trail is a strenuous hike for adults, with huge payoffs for adults in respect of its great scenery, wildlife such as hummingbirds and butterflies, and fascinating Inca architecture culminating in Machu Picchu. I don't deny that a motivated and fit 5-year old could probably manage the physical effort, but I would be very concerned about the risk of altitude illness. Children are MUCH more susceptible to this than adults, and anyway not good at communicating their exact symptoms. And a sick child in a remote part of Peru is an avoidable emergency.
But I'd be very worried about any travel agency who didn't query the plan to take such a young child on such a long trek – among other reasons because I'd expect the average 5-year old to be bored stiff during day-on-day hiking. And a bored child is a disruptive child!
