I had a very smart nun when in the 3rd grade. She asked the children to "take up a good habit" for lent, instead of giving something up. She suggested helping elderly neighbors, reading bible each night, or helping a younger sibling. The thought was that after 40 days, the new habit would continue. When kids are asked to give something up, they resent it and go right back to at Easter.
So what are you TAKING UP this lent may be a better question.