Mathilde B. answered 02/23/20
Success in Spanish for College, High School (AP & IB) + Middle School
Mijo and mija are contractions of mi + hijo and mi + hija. We use contractions in English too, just a little differently. Don't is a contraction of do + not. A less formal but common contraction is (though technically incorrect) gotta - got + to.
Mijito and mijita are essentially the same, except the diminutive suffix ito or ita is added to the end of hijo. A diminutive sometimes implies that something is small, but it also shows affection, like calling someone a "darling" or "dear".