How old are the kids? How are your swimming skills? If you needed to split up, I'd split them by swimming skill. The flying jib slide is *probably* not a good idea for your beginning swimmers, but the kiddie slide would be good. The harder issue is where you'd leave your stuff! If all 3 kids can swim, but just at varying levels, the only issues for you are the slides (because the entry is across the walkway, and the big slide is a dark tube for much of the time, so could be scary), and the lazy river, which is all deep and a decent current. Even though there are lifeguards all over the place and they are top notch, I would want to be in the lazy river with the kids, especially the not-so-strong swimmers.
Background - DH and I are both strong swimmers; I used to lifeguard and teach swimming. When we were there with our 6yo and 2yo, the 6yo was a beginning swimmer (a decent swimmer for her age, but she was 6) and the 2yo was not a swimmer at all. DH and I had to split up. The 2yo was pretty much only in the sandy bottom zero entry area, but she would fall down at a moment's notice, go under water, and I would pull her up and she'd be laughing. Our 6yo tried everything, but of course an adult needed to go with her to the slide entry, across the walkway to epcot, and she wanted us to wait for her at the bottom of the flying jib slide. She also really liked the lazy river. It's not really relaxing if the kids will need you to be nearby - so we will wait until the toddler is a strong swimmer and then we will stay there again. My older daughter (7) is now a strong swimmer, but I would still want to be with her in the lazy river and the slide entry.