We already know that children are quick to catch on to skiing. But if you also want them to acquire a good technique, the best option are the resort ski schools, some of them quite longstanding. They help kids to perform the wedge for the first time or to perfect their technique. It is in fact quite common for many schools to take their pupils to a resort for a few days so that they can learn to ski. If you do not want them to learn within a group, you always have the choice of hiring an instructor.
Check with the Catalan ski resorts, because they all have a ski school.