Some people have explained but not quite like you’re 5, so…
When you’re a baby, you can’t make many sounds. The easiest sound to make is “ma ma ma ma” and “pa pa pa” or “ba ba ba”. Mummies and daddies heard babies make these noises and thought that the babies were talking about them! So, forever since long ago, mummies and daddies have agreed with babies when they point at a person and “Mama! Mama!”
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