What is the ruling on hanging educational posters that contain pictures (such as pictures of alphabet letters along with pictures for each letter) in children's rooms?

There is no harm in teaching children letters by writing the letter with an appropriate image, even if the image is of animate beings. This is permissible due to the concession granted for "girls' play," and because young children are allowed things that adults are not. Displaying these images is not problematic because it is permitted, and because the intention of veneration is absent from them.