Choose Eilean Donan if your family wants the west-coast setting, a bridge-and-views stop and a short look around a historic castle. It offers more than a roadside photo if your children enjoy stories and historic places, but there is no play equipment or easy indoor fallback.
If you are travelling between Inverness and Skye, Loch Ness and Urquhart Castle is the more substantial castle visit, with a visitor centre and café but also a steeper outdoor route. Eilean Donan is the shorter, more scenic option, so do not add it as a detour just to fill a day.
For a longer stay around Dornie or Kyle of Lochalsh, consider Glenelg brochs, Lochalsh Woodland Garden at Balmacara or Falls of Glomach. Check each place’s access and weather before adding it.