Mothering Sunday in the UK and Ireland falls on the fourth Sunday in Lent, so the date varies a little from year to year dependent on Easter in the Christian calendar.
Many countries and cultures have a similar tradition and although it is often referred to as Mothers' Day it has no connection with the American festival of that name which falls in May. Traditionally it was a day when children who had gone to work as domestic servants or boy apprentices - sometimes as young as 10 - were given a day off to visit their mother and family.
Most sources agree this evolved from an earlier custom when people returned to their home or 'mother' church once a year, usually in the middle of Lent when many folk attended the main church or cathedral in the area, rather than their usual local parish church.
Inevitably, the return to the mother church became an occasion for a family reunion when children working away returned home. As they walked through the countryside some would pick wild flowers to give their mother as a small token.
The revival early last century of Mothers' Day in the US is most often attributed to Anna Jarvis... read more here and make up your mind whether you prefer Mothering Sunday or the less formal Mothers' Day! http://www.history.com/topics/holidays/mothers-day