That is because Mother's Day as it is called now [which is another marketing ploy] is a corruption from the religious "Mothering Sunday" it has nothing to do with parents but is a day for honouring mother churches, and so should be the 4th Sunday of lentWith Mothers Day, US and Australia have it 2nd Sunday in May - UK have it different Sunday every year
dont thank me I am a pagan, the OH was dragged up catholic by a bunch of penguinsThank you,