With joint annual membership currently costing £82 (cheaper single and over 60 options available) my husband and I can visit all English Heritage properties at no extra cost (with the exception of a few events) and are allowed to take six children apiece for free! (Shouldn’t really make that public in case friends, or even complete strangers start dropping their kids off to us for the odd day out). We usually just take our son.
Our favourite haunts include Audley End, Dover Castle, Kent (including wartime tunnels), Tilbury Fort, Down House (Charles Darwin’s pad), Lullingstone Roman Villa and Kenilworth Castle (amazing ruins and Elizabethan gardens). Recently visited Great Yarmouth Row Houses for the first time, which proved really interesting.
English Heritage has a host of properties nationwide, offering in our experience, a very friendly welcome.