Agree with other replies to your post re: Twin Grove CG. It is very nice but may be a bit far a way. Hershey Highmeadow - we've never stayed there but a friend of mine does and likes it. If proximity to Harrisburg is required then I'd also consider Western Village RV Park in Carlisle. I've seen opinions here and rvparkreviews.com that run the whole spectrum but our experience was very good.
We have experience with only two CG's in the Lancaster area so far - Old Mill Stream and the Jellystone Park at Quarryville. The latter is aimed at families/kids like Twin Grove and is quite pricey. Old Mill Stream is right next to Dutch Wonderland; we've not been there since our pop-up days (about 18 years maybe). What I recall is an older CG with unusual layouts (in a "T" shape) for the sites.
Enjoy no matter which one you pick. Safe travels.