In mainstream parish Masses, it is recommended that the priest should address children present. I’ve only ever known one priest who did this consistently:
17. Nevertheless, in Masses of this kind it is necessary to take great care that the children present do not feel neglected because of their inability to participate or to understand what happens and what is proclaimed in the celebration. Some account should be taken of their presence: for example, by speaking to them directly in the introductory comments (as at the beginning and the end of Mass) and at some point in the homily.
My parish does celebrate a children’s liturgy of the word. Here it is suggested:
Sometimes, moreover, if the place itself and the nature of the community permit, it will be appropriate to celebrate the liturgy of the word, including a homily, with the children in a separate, but not too distant, room. Then, before the eucharistic liturgy begins, the children are led to the place where the adults have meanwhile celebrated their own liturgy of the word.
Comments?
Catholic Sensibility 
The only time I’ve seen this it was kind of condescending and inappropriately done. I’m sure it could be done appropriately, but talking to the kids about Blues Clues at the beginning of Mass isn’t the way to foster children into a good liturgical mindset.
So n. 17 mentions a “homily”. I’m curious how n. 24 corresponds to that, as far as a lay person speaking to the children after the Gospel: is that in place of the homily, is that a “homily”, or is it before the homily?
The difference is #17 would be the mainstream parish Mass, probably Sunday Mass most often. #24 is the situation in which the assembly is mostly children with few adults.
Though the new canon law was still ten years away at this point, I’d say there was less of a definition of homily as a clergy-only exercise. Clearly the DMC was operating under the higher priority of the needs of the children in the assembly: if a priest would be incapable, it would be logical to select someone who could preach to children.