Sing a song. One of the easiest and most common ways to teach preschoolers vowel sounds is with the alphabet song. But there are tons of other phonics and alphabet songs available. Choose songs that will be easy for your preschoolers to learn and sing. Set a time for sing-a-long each day to reinforce the sounds.
Read aloud to your child. Children learn letters and sounds by repeatedly seeing and hearing them. Choose rhyming books for story time that emphasize letters and sounds. Books by Dr. Seuss work perfectly for this activity. As you read a word that has a particular vowel sound, point to the letter, repeat the sound and have your child mimic the sound. Switch books occasionally to introduce your child to new words and sounds but be sure to continue to read old favorites.
Use flashcards with pictures. Present your child with cards that have the vowel, a word that includes the letter and a picture of the object. For example, if you are teaching the short A sound, you would use a card with the letter A, the word "bat," and a picture of a bat. Point to the letter, demonstrate the sound it makes and have the children repeat the sound. Once your child has properly made the sound, introduce the whole word by saying it to her and having her repeat the word.