I have seen major sleep disruptions happen out of nowhere in my kids, but having it happen for both kids at once would lead me to consider looking into different things that what I think usually cause ours. Ours will happen following an illness sometimes, like they got really out of whack on schedule & are struggling to get back on. Teething & yes even at these ages, there are teeth issues until up to about 13 or so, even new molars, depending on how a child cuts them. Growth spurts can cause it too, especially with growing pains if those are an issue, but I've seen it even in absence of any "pains". Also time changes, but I can't imagine you had one of those in this time period you are talking about.
So outside of those, other things that could be relatively benign and perhaps impact two children at once, would be things like a really scary thing, a movie, story, something they witnessed or something that happened that scared them. When I say witnessed, I mean it doesn't need to be something actually awful, just something they perceived as scary, such as when I saw my brother fall out of a tree. He was fine. It really was upsetting to me for a long time after.
And on to the less benign, which is of course that someone has legitimately done something to the kids or in front of them that is totally inappropriate. If this didn't start right with camp, that doesn't mean it wouldn't be at camp, since it didn't have to happen on day one. And as much as you think your kids will tell you if something happens, you might be surprised. My son was left at a park with another mother so I could handle something for ten minutes. That is all. I cam back, everything was fine, we went on.
Then a few days later he started asking me weird things. I made no link. He asked me if I liked his hair. I was not initially alarmed that he asked. I did ask why he asked. He said "No reason, just wondering". Then another week or so passes & he tells me he wants to cut it (he was growing it out). I was super surprised by this out of nowhere so I asked again, and he gave me some vague things about wanting to try it short. I told him fine, but I wanted him to give it one week to think about it, since he had been growing it two years, and if he changed his mind, that is a long time to get back to this length.
One week later he says again he wants it cut. I pushed a little harder as this didn't seem typical for him & then finally he tells me that when I left him for those 10 mins, that lady's daughter & her 2 friends (older than him by several ears) cornered him on top of a play scape area, held him down & put lipgloss on him & told him if he wanted long hair like a girl he should wear makeup like one too. I was so shocked. I was shocked that this happened so quickly, shocked this girl did that and that he held that in for two weeks. He was only 6. He told me that he didn't tell me because he was embarrassed, he didn't want to talk about it, and that he was afraid if he got her into trouble, she would be even more mean in the future.
So, I tell you all that to say that just because they haven't said why they are upset, there very well could be a child, an adult, whoever that has done something very upsetting. When he told me, I also had realized he had been sleeping bad, more bad dreams, and in general more ornery. He was also cutting 6year molars so I had wrongly chalked it up to that.