Sunday's are called to be a day of rest.
As God commanded us in Exodus:
Remember the sabbath day, to keep it holy. Six days you shall labor, and do all your work; but the seventh day is a sabbath to the Lord your God; in it you shall not do any work.
2184 Just as God "rested on the seventh day from all his work which he had done," [Gen 2:2] human life has a rhythm of work and rest. The institution of the Lord's Day helps everyone enjoy adequate rest and leisure to cultivate their familial, cultural, social, and religious lives. [Cf. GS 67 § 3] Growing up, my family always had Sundays set aside for relaxing and family functions. We didn't plan much, just enjoyed the day together.
2185 On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord's Day, the performance of the works of mercy, and the appropriate relaxation of mind and body. [Cf. CIC, can. 120] Family needs or important social service can legitimately excuse from the obligation of Sunday rest. The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health. 
The charity of truth seeks holy leisure; the necessity of charity accepts just work. [St. Augustine, De civ. Dei 19, 19: PL 41, 647]
Since getting married, Carl & I have often not been as good about our day of rest. We have tended to use Sundays to get caught up... on yardwork, on housework, on book work... As the girls have gotten older, the urge to reclaim Sunday's for our family has gotten stronger and we've made a significant effort at doing so.
I won't lie - we still use Sundays a little bit for catch-up, but at a much more leisurely pace. Yesterday for instance we spent most of the day outside. It was such a beautiful fall day, we knew we didn't want to be inside for most of it parked in front of the TV. And we actually went out without much of a plan as to what our "intent" for outside time was.
It unfolded to be about one of the most perfect days as a family that I've had in a REALLY long time. One of those types of days that will live in my memory and hopefully in my kids memories as well. Not because anything extraordinary happened, in fact nothing out of the ordinary happened... but we lived the day. We played, we worked, we stopped working to enjoy the kids, we "worked" with the kids, and we played some more.
The joy on their faces racing around the yard trying to get their kites to fly.
Snuggling with Daisy cat.
Helping their Daddy unload the pickup of all the dried out corn stalks.
Eating dirty carrots that I had just pulled from the garden.
Using their chalk to "paint" their clubhouse, then to color Lauren's little plastic slide.
While Carl washed the pickup, they washed their trikes, and their toy cars, and the plastic slide... just about anything they felt like scrubbing with a sponge!
Visiting with some friends that stopped by to get some pumpkins and watching their eight year old play with the girls.
The smell of their freshly washed hair after we came inside and snuggled on the couch for a few minutes of Mickey Mouse Clubhouse before they ate dinner.
Thank you God for this glorious day!