My kids are going into 4th, 2nd, and pre-K. They're going to be doing a few morning camp programs, and the older 2 will be learning there. (9 year old is mostly signed up for science and technology camps since that's what he's into, and 7 year old is doing an extended school year/special needs program through the public schools.)
I'm with Juli on themes being an easier way to plan. On the weeks when we don't have camps, I may try to do a few themed weeks that will appeal to all 3 of my kids and lend themselves to some learning under the guise of fun. No idea what the themes might be yet--a few that come to mind right away are space, architecture/building, and restaurant week (let the kids run their own restaurant and take our orders, help cook, etc.). Maybe something ocean related, too since they all like dolphins and were obsessed with Winter the Dolphin for a while. If we were doing a cooking project for restaurant week I'd let my oldest adjust a recipe (like change it from 2 servings to 4) to practice fractions, then let my 2nd grader help count money when I paid my bill.
I'm planning to look into some learning apps, especially for math, that they might have fun playing. I've never played Words With Friends, but I wonder if that might be something spelling related that I could get the boys playing with extended family members. In the past we've also done the
JumpStart website (an educational video game) and all 3 kids enjoyed it. 4th grade is still within their target audience, so that may be one of their screen time options. Jumpstart also has a
section with free activities, lesson plans, resources, and worksheets. I think you can browse by grade or topic, but I'm not sure what's there.