How can i help my 3yr old not have such a big bm i know its got to hurt her bottom..is there anything to give her?

Water: Water is one of the best ways to be sure you are getting enough fluids and subsequently normal bowel movements. Fiber also helps with regular and softer bowel movements. Unfortunately large painful bowel movements can be linked to constipation, or lack of regular bowel movements. It can also be a sign of stool holding or in rare cases (hirshsprungs) and underlying condition. Try fluids first!