Captain reported a track deviation after takeoff from CVG. The crew navigated to KENNL but they were cleared to the similar sounding KENLN

Narrative

The first 2 fixes on our flight plan were KENLN and KENLL. Shortly after takeoff we were cleared direct KENLN. We mistakenly entered KENLL. A few minutes later ATC said he showed us diverging from our course and gave us a heading to reintercept.Similar sounding and spelled fixes in sequence on the flight plan. High workload phase of flight with weather and moderate turbulence. The turbulence combined with the interface of the trackball and cursor was also a contributing factor. While hovering over KENLN with the trackball and cursor; I asked the Flying Pilot if the fix looked correct and he acknowledged. I think in the time from initially moving the cursor; asking for acknowledgment; selecting it and then executing it that my hand moved the cursor just slightly enough from the turbulence that it hovered over KENLL when I actually selected and executed it. Because the spellings were so similar we didn't notice the different fix on the PFD (Primary Flight Display) area when verifying we had turned direct.A reintercept heading was issued by the controller. We realized what had happened and told the controller we were able to go back direct KENLN and he issued that clearance. The controller asked if we had mistakenly entered KENLL. We acknowledged that was what had happened and apologized; he said no problem".It would be beneficial to add similar sounding and spelled fixes to the threat forward briefing. Also in the future I will select the fix first and then ask for confirmation before executing so that cursor / trackball movement cannot interfere; rather than just hovering over it with the trackball for confirmation."