But is there anything "wrong" with this?
No. I have certainly never encountered it in traditionally Orthodox lands, though.
Personally, I find it didactically useful as since if the homily is delivered in such a way as speaking to kids, then even adults can understand plainly.
One priest I know regularly gives children's homilies, usually explaining something tangible (e.g. what is that "Tabernacle" thing on the Holy Table; why is the Icon of Christ the way it is; what are the names of the different priestly vestments and what do they symbolize, etc.). Many parishioners remark that they prefer these to the normal homilies.