The usual starting age
Most UK riding schools take children from around four or five years old for a structured lesson. Before that, the balance, attention span and ability to follow instructions a lesson needs are not quite there. Plenty of yards do offer lead-rein pony rides and "own a pony" mornings for younger children, where the experience is about sitting on, being led, and getting comfortable around horses rather than learning to ride.
Under-fives
Some centres welcome under-fives specifically, usually on a lead rein with a parent walking alongside. More than 100 yards on Saddl are set up to take under-fives, and you can filter for yards that accept under-fives or browse family-friendly riding to find one near you.
What a young child needs
Not much to start. The school provides a properly fitted helmet, so you do not need to buy one. Bring long trousers and footwear with a small heel, or borrow boots at the yard. First lessons for young children are usually short, often half an hour, and either on a lead rein or in an enclosed arena with the instructor close by.
Building up
By seven or eight, most children can join group lessons and start coming off the lead rein. From there it is rising trot, a bit of independence, and, for the keen ones, pony days and holiday camps in the school breaks. Progress is individual, so a good yard moves each child on at their own pace.
It is never too late
There is no upper age limit. Teenagers and adults can start at any time, and riding is one of the few sports you can take up later in life and still enjoy for decades. If you are starting as a family, many yards will teach parent and child alike.
Finding the right yard
For a young child's first lessons, look for a yard that teaches children regularly, has calm ponies, and ideally holds BHS or ABRS approval. You can search riding schools near you on Saddl and see which welcome children and under-fives.