In the first half of XX century in USSR there was a burst of poetry for children. Many highest level professional poets agreed that poetry for children (if done in a proper way)is much more demanding to the quality than any other kind of poetry. There were many theoretical background around it and the highest level of standards has been settled. There are such names as Marshak, Chukovsky, Kharms, Mikhalkov etc.

Poems:
Marshak
Chukovsky
Kharms