If he is 2-3 or older I say, thats my real name. But you call me mama or mommy (you choose what you want him to call you). Most kids experiment with their parents first name for the heck of it. You are not discouraging a word. He can call you mama, but every day ask him "whats my real name". You can say your real name is...daddy's real name is...mama real name is. So he keeps your name as part of his speech but you only answer to mama.