I have 2 trailgators (Thanks GerryLAger), I use an old road tyre to save the kids headtube and the seatpost. I do have an old sacaficial seatpost for each bike (with comfy saddle), but mainly because the bolts can stick out a bit and I prefer not have the weight on the back of the bike if I’m not towing. TO swap over takes 30 seconds a bike.
It massively extends the range you can go with kids (literally) in tow.
My 8yo is good for a couple of miles before she is tired and the 5 year old has just learnt how to cycle. So we tow them to the local trails/pub/skatepark/wildlife place, let them cycle around until tired and then tow them back.