The short answer
A Clydesdale is temperamentally one of the loveliest horses a child will ever meet, and physically one of the least suitable for her to manage. Both halves of that sentence matter. As a supervised ride and a horse to groom, fuss over and lead a few steps with an adult on the rope, a steady Clydesdale gives children an experience they remember for years. As a child's own horse, to catch, tack up, lead and ride independently, his sheer size defeats the project before it starts.
A patient nature around kids
There is a reason Clydesdales appear at shows, fairs and therapy settings surrounded by small visitors. The breed's default setting is unhurried tolerance: most will stand square and sigh while a child brushes the same patch of shoulder twenty times, reaches up to pat a knee, or presents a carrot with a flat, nervous hand. They are rarely sharp, rarely quick and rarely offended by noise or crowding. For a child who is frightened of horses, a quiet Clydesdale's calm can be the thing that melts the fear, because the horse radiates the sense that nothing is about to happen quickly.
Height and handling reality
Then there is the tape measure. At sixteen to eighteen hands, a Clydesdale's back is above most adults' heads, let alone a child's. She cannot groom his top half, cannot lift a saddle anywhere near his back, cannot bridle him, and cannot reach his head if he raises it. On a lead rope, a horse of that weight who decides to drift toward interesting grass simply takes a child with him, however kind his intentions. From the saddle, the fall is the longest in the horse world. None of this is the horse's fault; it is physics, and physics does not grade on temperament.
The shared family horse model
Where Clydesdales succeed with children is as the family's horse rather than the child's horse. Adults catch, groom, tack up and lead; the child rides in an arena or on a led hack, grooms everything within reach from a step stool, learns to pick up a very large foot with two hands and an adult beside her, and absorbs how a big horse is managed. Older, taller teenagers can take on progressively more of the groundwork, and by the time a young person can genuinely handle a Clydesdale, she has skills that transfer to any horse alive. Shared this way, the breed's patience becomes a real asset instead of a trap.
The better first step, and when to choose the giant anyway
For a child whose main wish is a horse of her own to do everything with, an appropriately sized pony or small horse still wins easily, because independence is the curriculum. Choose the Clydesdale when the honest plan is a family horse the adults wanted anyway, with children as supervised participants. In that household, everyone needs the same information about his feeding, shoeing and handling quirks, kept where the whole family can see it. KinsLe's Family Sharing has a straightforward role here: you share his profile with a spouse, grown-up son or daughter, or teenage helper you pick, so each of them can reach the Clydesdale's profile without going through you.