The word "onomatopoeia" comes from the Greek and, translated, literally means "the name of the sound." Many young readers who started with the works of Dr. Seuss, for example, are familiar with these sounds, from such books as "Mr. Brown Can Moo! Can You?" Children start out by hearing the sounds as the teacher reads a book with onomatopoeia in the story, or from a list of sounds, then make the sounds out loud and finally move to writing them out, copying them from the book and writing them independently.
Several online resources exist that allow students to view phonic units, click on them and hear the sound. Then, they write down the sound that they just heard. These units include individual letters, vowel-consonant combinations, diphthongs and longer chunks of sound. Seeing and hearing the sound simultaneously before writing it helps learners who need visual as well as auditory cues to learn the connection.
If you have a toddler whom you would like to teach to read, you can buy magnetic letters for your refrigerator or dishwasher. However, you don't want the plastic letters that just stick to the wall -- there are magnetic sets that come with one mount for the refrigerator and with computerized letters you can slide into the mount and press a button. When you push the button, a voice will read the letter on the front and make the phonic sound. Get your youngster a sheet of paper and some markers and help her practice writing out each letter after hearing it.
While it's important to know that "ough" can sound like /off/, /o(long)/ or /oo(long)/, the next step involves combining that with preceding letters to make words like "cough" or "through." Have students practice writing longer words by reading them one phonic chunk at a time while students write. This is an important bridge between initial phonics instruction and actual reading.