The Waldorf idea about toys for children, is that they are simple and made of good quality natural material.
The child needs to be able to fill in with it's imagination. This would mean, that the child decides, for instance, the mood or age of the doll.
From a pedagogical point of view, I would say, 4 to 7 years old is the perfect age to give a MonPilou doll, to your child. The baby doll is suitable for a younger (not mouthing) child. Make the moment of giving special and be an example, in taking care of the doll. You could put the doll, as a surprise, in a doll bed, next to your child's bed (maybe with candlelight) so, it will find the doll, when he or she goes to bed. And once in a while, you could make or buy something new for the doll, together with your child (for example, baking doll cookies of salt dough or make a little bracelet). This will keep doll play alive.
Waldorf dolls find their origin in Waldorf education/school, founded bij Rudolf Steiner. He was an important thinker/philosopher around the 1920's. His philosophy is called Antroposophy. There are many Waldorf- or Steiner schools, all over the world.
Better Things In a Better Way.