Of course, this concept could work for a tender of any sort, so I thought it worth sharing. I've seen them built of everything from angle iron to PVC to copper pipe fittings; only imagination limits the options.
Sure, you can buy them in the store, but most I've seen are home-built. These took a few hours to puzzle out and piece together; a good father-daughter project, better than time plopped in front of the TV or... on the internet.
The lumber is 3/4" x 8" boards left over from a shelving project. We screwed them together with deck screws; I got lazy on the pre-drilling on the one side and the board split a bit, though it doesn't seem to have made a difference. The curve was transferred from the kayak to the saddles using a compass (the front and rear saddles are slightly different). The axle is a length of 1/2" brass rod left over from something, threaded on each end. The wheels are Home Depot mower wheels for ~ $15.00, the only bit I couldn't find on the scrap heap.
The foam was cut from a scrap work-out mat tile. The pipe stubs are scrap 3/4" PVC and fit into drainage holes molded into the kayak hull--these prevent shifting.
The wheels are lashed to the kayak with 1/2-inch line and a snug truckers hitch. I did a sloppy job in the picture--lightening was starting to flash. They normally cris-cross between the axle and the wooden frame.
We throw all our gear in the kayak, grab the handle, and start walking. Miles are possible on a good path, and we have done just that on occasion to reach a prime spot. More often, it's a matter of a few hundred yards. Sure, a sturdy person can heft a kayak on a shoulder, but a second trip will be needed for a day's worth of gear. With the wheels a child (or a tired adult) can tote the works. Well worth a little shop time, and I enjoy turning scraps into something useful.