Why does the dates of Easter change every year? Why is not the same Sunday every year like Mother's Day and Father's Day?

Not only does Easter dates vary in the USA it varies across the contents. The difference is between Gregorian calendar and places like Greece, which use the Julian calendar for Orthodox feast days.

Easter is the day that we Christians celebrates the resurrection of Jesus Christ after his death on the cross. Easter falls at the end of 40 days of Lent and is always the Sunday after Good Friday, which commemorates the death of Christ.

Easter falls the first Sunday after that full moon.

Full Moons change every year so the Easter Bunny doesn't work the same evening every year so he and Santa's work schedule are not alike at all.