I don't think you have to take kids out everyday. Sometimes the "mom" guilt meter goes off and you question yourself, if you are doing enough, etc. I used to ask myself the same question; I still ask that, my kids are only 4 and 6, and I always try to make sure they have at least one thing going on (karate once a week, piano, etc). I try to have just enough, not too much.
I think it's good to have kids in activities (preschool, sports, music classes, etc) and I also think good ol' playing outdoors is very important too, simple walks or playing at a local park. I wouldn't feel bad about wanting a day to just stay home. Try to have an activity planned (something you don't normally do) or go in your front and backyard and do something you wouldn't normally do on the day you want to stay home. Make it an event and your son will look at it like a class that he goes to weekly.
I would go through phases where I felt like I wasn't doing enough (what I call the "mom guilt meter"),then I would sign my kids up for a bunch of stuff, be busy everyday and fill in between times with playdates, etc. I got burnt out and so did my kids. A nice moderation is best.
Your son is still young, soon enough he will be in elementary school and be gone all day; then you will be begging for the days when was at home with you and full of energy...
Not sure if I helped but I wish you the best of luck.