Praise be to Allah.
There is nothing wrong with teaching children the alphabet by writing letters with appropriate pictures, even if they are pictures of animate beings, because of the concession allowing “dolls for girls”, and because concessions may be granted to small children that are not granted to adults. Putting up these pictures will not do any harm, because they are images that are permitted, unless the pictures are put up with the aim of venerating the images themselves; if there is no such intention and the pictures are permitted, there is nothing wrong with having them on the ground or hung on the wall.
See also question no. 20325
And Allah knows best.
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