I would tell them the truth. You don't feel you have enough time at home with your daughter, so that's what you are going to choose to do for now. You want the kids to have a teacher that is going to devote more dedicated time to them, and the best way to make sure that happens is to step down. To your husband: You can always teach later, but your daughter is only going to be young once.
IMO, the only reason to work instead of stay home with your kids is 1 - if you have to financially, or 2 - if your job fulfills you and makes you a happier person. If neither one of these is the reason you are working, then it sounds like you are making the right decision. Just because you can do something doesn't mean you should if you don't want to. And remember, you don't always have to justify your choices, and you're allowed to change your mind.
I don't think you are a wimp at all. Being a SAHM is the hardest job I've ever had! If you're not happy with your situation, and have the financial means to change it, then I would absolutely do the same thing.
IMO, the only reason to work instead of stay home with your kids is 1 - if you have to financially, or 2 - if your job fulfills you and makes you a happier person. If neither one of these is the reason you are working, then it sounds like you are making the right decision. Just because you can do something doesn't mean you should if you don't want to. And remember, you don't always have to justify your choices, and you're allowed to change your mind.
I don't think you are a wimp at all. Being a SAHM is the hardest job I've ever had! If you're not happy with your situation, and have the financial means to change it, then I would absolutely do the same thing.