We are looking at visiting a couple Islands, doing a day trip with a stop at multiple. We saw some tours on viator but was curious about setting things at our own pace and what it would cost and the way to go about renting a speedboat that someone could take us around.
We will also have kids with us, and some of them seem to be focused around adults and age limits
I have not done this but I am sure it is possible--you could take a walk around the waterfront and probably find someone, but every town has a tourist office so I would check there. Also once you book accommodations, ask them as well. There could also be local excursions that are more in line with what you are looking for. When I was on Hvar it was fairly informal, they had day boats going over to the Pakleni islands, which was a nice day out.