Our boys alternate between mom (or rarely mommy) and dad (daddy) and our first names. For our oldest it's now almost exclusively first names. I and my siblings ALWAYS called our parents by their first names, NEVER "mom" and "dad" or anything similar, and still do, so our kids are used to hearing us do that, and they know it's ok with us if they do that with us too. So they seem to be heading to that choice.