The ACSI app doesn't use an interweb connection. You download the database for off line use. So 3G doesn't come into it. The app also includes non ACSI sites so covers a lot broader set of sites. Also useful for us, you can put a filters on your search and see the sites on a map. Out of season on our current trip this let's us see which sites are still open in the area we're going to next.
Probably not much use for a family with kids but very useful for people touring out of season is the motorhome parkings app. Again you can set filters on a search, so can easily restrict the list to those with WCs.

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Another great app for anyone wanting off line maps is maps.me. this also shows footpaths. We use it all the time. In Italy last week we came across a new bypass with typically awful signage. Whipped out the tablet (after we'd parked up of course) hit the current location button and hey presto we knew immediately where we needed to be. We also use it in towns were visiting for example we were in Perugia day before yesterday and you can quickly get a navigation fix.