I've only spent one night there when on a boat delivery trip on the west coast, but it was quiet and peaceful.

Most small islands have a strange sort of charm, perhaps it's the isolation after the last ferry has sailed for the day. Unlikely to be too cold on the west coast at sea level, but do take waterproofs and wellies.
I suppose it depends on their ages, but I would think there would be an overload of things for children to do if you can get them interested.
Probing in rockpools, fishing off the rocks, identifying the shells and shellfish, beachcombing, looking under rocks for wee crabs and things, making boats from driftwood and sending them on their way, messages in bottles(if still environmentally friendly), identifying seabirds and land birds, being the first to spot one of the famous breed of Luing coo, sealspotting, collecting driftwood to create a fire to make the tea, observational things like timing the period between high tide and low tide, pretty exhausting I would say

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Enjoy!