i'm jealous - there's loads to do, some of which have already been mentioned.
green welly stop on the way to oban - bit tacky but a must!
sealife centre at oban (if you've parked in a pay and display car park in oban then you get money off the entrance fee with the ticket).
if you like sea food then there's a wee hut near the ferry terminal which sells freshely caught seafood - they also have large crabs which you think are 'sleeping' but are actually alive! DP had the most amazing scallops from here (i can't eat seafood)
you can visit loads of the islands - some of them include kererra, lismore, mull (lots to do - castles/beaches/train/animal/sealife adventures/good food try the fish van at the pier in tobermory mmmmm), iona - can climb the hill for fantstic views, visit the abbey, the beaches are incredible - the bay at teh back of the ocean (nothing between you and america). isle of seil and easdale (good beer!) short 5 min ferry to the island - kids love it. and there's a good seafari from here. lots of places to stop and do stuff.
rare breeds (quite hilly) but if DCs like animals it's worth it.
glencoe - scenery/walks/waterfalls/clachaig inn - bits of harry potter was filmed near here (if DCs are interested in HP).
the power station inside the hill - cruachan (i think!)
so much more but DD2 is waking up - check out visitscotlands website as well...
oh and to stop the midges - get some avon skin so soft oil - original fragrance (i think woodland fresh?) - works a treat (hillwalkers/army etc all use it when on the west coast)