Children will often make mistakes with their words when they are learning to talk. If it was pointed out every time that they were saying it wrong, the child could become reluctant to try new words and have reduced self esteem.
Simply repeat the word back to them correctly so that they can hear how it should be said.
Child: "goggy" Adult: "Yes, there's a doggy you're right!" This not only rewards them for their attempt at saying the correct word, but also allows them to hear the sounds said correctly so that they can learn how it should be said in a positive way.