E.,
You are 100% right. Please have your husband read this and everyone else's responses.
I also have three kids, and my oldest will also start kindergarten in a couple weeks. While your husband is right about it being a hassle to get out of the house, he is missing out on being a dad and doing family activities together!! Tell your husband that nothing in life is easy and life is what you make of it. Yes, a lot of planning goes into it, but why would your husband care if you are the one who packs snacks, replenishes the diaper bag, brings formula and a bottle (if you have a baby), makes sure the strollers are in the car, etc??
Also, don't forget the camera!! The second all of you and everything are in the car and you are backing out of the driveway, it is all worth it! I know you know that, but your husband needs to know that!
Doesn't your husband want memories of the five of you now, as opposed to five years from now? Even if the kids don't remember what you do, that's okay! It is all part of their childhood development. They had fun at that moment in time, even if they are only 2 and won't remember. Tell your husband he is missing the point!!! It is about experiencing life as a family, and your kindergarter will DEFINATELY remember, and you don't want him to get cheated out of the family fun stuff just because he has younger siblings!
Do you have a solid marriage? It doesn't seem like it. It doesn't make sense to me that your husband doesn't want to do family things together, just b/c the kids are young and it's a "hassle." I feel that there is more going on here, and only you know if this is true. Insteading of him booking you a weekend trip w/ your friend, all 5 of you should be taking this weekend trip! Is he trying to "get rid of you" for the weekend? Does he not want you around? It seems a bit suspicious to me. Someone else suggested marriage counseling. I agree. Best of luck and I hope your husband comes to his senses!!