On this page of the game guide to Borderlands 2 you will find a detailed description of the side mission titled Best Mother's Day Ever. You can begin this quest in The Highlands by picking up the item named Taggart's Gift for Mom.
1) Taggart's Gift for Mom
2) Stalker nest/Henry
There is a chance that one of the Stalkers will drop a Taggart's Gift for Mom after being killed, picking up which will activate this mission. Personally I got it from a Stalker killed during The Overlooked: Medicine Man, around the area marked on the map as .
After you obtain the required item, drive to the Stalker nest in the northern part of the map . Kill six Ambush Stalkers to lure out Henry. As the enemy is surrounded by a shield, a Shock Elemental Effect weapon would by a good choice. Henry will from time to time summon Slagged Stalkers (use them for Second Wind) and teleport to regenerate his shield. Once he's head, pick up Taggart's Fist. Now place the chest in the designated spot and open it to collect the prize and finish the mission.