the background must be white. the the picture must be clear eg: if u r teaching vegetables. the flashcard backgroud will be white, the picture (ie: potato should be at the middle) would suggest real potato picture which you could google. the n the wholde set will be vegetables.

the word 'potato' can be write behind because you do not want them to confuse, but actually depends which type of kids your dealing if special child like autistic they might get distracted. or you also can print seperately so they can learn to match the word and picture.

size depends own individual i would say half size A4. buy the card material that u can print (normal priter) matte type not glossy cause consume more color.

If can afford try to get ipad they have a lot of flash card for toddlers. is easier and attracts the child