"Mom, I'm back."
お母さん is either used when addressing your own mother (politely) and when talking about somebody's mother (politely). It should not be confused with 母 which is used when talking about your mother to somebody (humbly).
お母さん: Polite 母: Humble
Copied and pasted from thoughco.com: The meaning of the Japanese word Tadaima is "I'm back home." However, the literal translation of tadaima from Japanese to English is actually “just now." It would be awarkard in English to say “just now” when arriving home, but in Japanese this phrase really means, “I just came home."
If that helps anyone to remember it! It always help to break up these phrases for me.