At the right price, there is a market for everything. The issue is a) is that price (usually not much on the dollar) worth your time to photograph, describe, post and monitor in order to sell it at the best (if not great) price or b) do you have better things to do with your time?
Built kits have essentially no market value unless you are a really top-notch and name builder. Museums might give you a tax receipt for them and that can be a pretty good deal, but, other than that, they are essentially worthless.
Parts and partially built kits are also essentially worthless unless you are willing to put a LOT of time into selling them.
Unbuilt kits are worth, generally 20-50% of new, depending on the kit. Newer kits are worth closer to 50%, but it rapidly falls off towards 20%. If it’s rare it might be worth more than what you paid, but don’t bet the farm on that being the case.
To maximise the return you need to use something like Ebay and make a really good posting., Lots of photos, good description and a reasonable price. But that’s a lot of work for each and every thing you try to sell.
If you just want to move them on, see if a local hobby shop will take the whole bunch for about 5-10% of retail value. Not much money, but they are off your hands and out the door.
If you leave them to your kids, they are going to end up in a dumpster so save them the hassle and put them all in a dumpster now.
If you belong to a club you could ask that they sell them for you at a show and agree to take 20-50% of whatever they get for them giving the rest of the money to the club, but that will still only end up with 5-15% of retail in your pocket.
It’s a harsh reality, but it’s reality nonetheless.