Let's get more details. Are you using an all-in-one curriculum? Is there one subject your 7 year old tends to do without much struggle? Is the work mostly online? Besides claiming she cannot do it, does she have any more specific complaints? How much time (if she buckled down) do you estimate she would be spending on her schoolwork?
I am constantly re-evaluating and trying to improve my homeschooling. My daughter was pushing back against math specifically, so I finally caved and got her a different curriculum. My son pushes back against writing, mostly, so I've found a way to structure in the kind of writing he prefers. Sometimes it feels like the little dutch boy, sticking fingers in the dike whenever a new leak springs up, but there are often weeks at a time where the dike isn't leaking, so it's okay.
One great thing here is that your kids are still quite young, and that a LOT can be learned at this age through reading and experience. I wouldn't sweat too much the "lost learning" if you can find other ways to acknowledge, celebrate, and encourage learning. If they're doing a lot of reading, that is the best thing possible. Seed the house with Horrible Histories and science encyclopedias and Unicorn Academy books. Gameschool some important math skills with some well-chosen board games (ThinkFun is a fantastic games publisher for mathematical thinking). I especially wouldn't abandon a math curriculum, but you could maybe look into something like BrainQuest for a while, just let your second grader choose two math pages each day, whatever she wants, to work on. (For my daughter, since her math skills are basically strong, I eventually got her this book to do instead of finishing out her math curriculum. I'll get her back to a traditional math curriculum eventually, but I really wanted to avoid the "I hate school" mentality that was starting to build).
Also, research unschooling, just a little. Yes, there are times when unschooling feels like people are just abandoning all responsibility in helping their kids grow and learn, but there are also unschoolers who can help you see how much kids learn when left to their own devices, and can artfully help build a beautiful learning environment in the home.