From Wikipedia - Mothering Sunday is a day honouring mother churches, the church where one is baptised and becomes "a child of the church", celebrated since the Middle Ages in the United Kingdom, Ireland and some Commonwealth countries on the fourth Sunday in Lent. On Mothering Sunday, Christians have historically visited their mother church—the church in which they received the sacrament of baptism. It gained popularity in response to the originally American Mother's Day, held later in the year. The holiday is often known as "Mother's Day" in the United Kingdom, and has become a secular celebration of mothers and motherhood.
So for me, first and foremost a visit to our local Cathedral, where daffodils are given to any woman who would like them, and then some of my children and their families will turn up for a lunch out before going back to see the other side of their families in the evening.