Mommy or Mom (Mummy & Mum in British English) are informal words usually used by children in place of their mother's name. In English speaking and many other cultures it's not normal for children to call their parents by their first names. In contrast sons and daughters are usually called by their first names, a nick name or a shortened version of their name ( Seb instead of Sebastian), therefore we don't really have alternative versions when addressing our own children.