The icy moons are of interest for exploration as part of the overall "follow the water" strategy of exploration that NASA (and others) have been exploring for some time. The "where else can water be found" is a major question in e.g. the US Planetary Science Decadal Survey (which is a community-driven consensus document which outlines the questions of interest and the mission priorities for the next decade), ESA's Cosmic Vision 2015-2025 and the NASA Planetary Science "Big Questions" overview.
The "Roadmaps to Ocean Worlds" team (public overview here) laid out the goals of the ocean worlds program in 2018 and the overview graphic sets out the motivations and the path forward:
So the main targets are Europa, Ganymede and Callisto (icy moons of Jupiter) and Enceladus and Titan (icy moons of Saturn) with other "honorable mentions" for Mimas, Triton and Pluto and Ceres as detailed a little more in this NASA JPL infographic. Most of these destinations are in the "Characterize Oceans" and "Assess Habitability" stages of needing new missions, instruments and data to guide the future search for life.
Ocean Worlds destinations were added, somewhat controversially at a late stage, to the NASA New Frontiers 4 competition for mid-size missions (cost cap ~$900M; NASA New Frontiers program page) which was subsequently won by the Dragonfly mission which will go to Saturn's icy moon of Titan. Europa is the target of the NASA Europa Clipper mission which has followed a separate path of development, in some part at the urging of former Representative John Culberson, and ESA's JUICE - JUpiter ICy moons Explorer -mission, which will study Ganymede, Callisto and Europa (along with Jupiter itself)