In reply to Jonny Platt:
It depends on how old / fit / keen the kids are, really.
The above two answers are good; other, slightly longer Munro options would be Maol-Chean Dearg from Annat, or just a little North of Torridon, Slioch from Incheril - both fine hills with no real difficulty, but with longer approaches than Beinn Alligin.
You mention a less than ideal forecast - remember that there are a lot of great smaller hills there which might be below the clouds even if the Munros aren't, such as the aforementioned Beinn Damh, or:
- Meall a' Ghiuthais and Ruadh-stac Beag, to the North of Beinn Eighe
- The unassuming Sgorr nan Lochan Uaine and Sgurr Dubh on the South side of the glen, delightful hills which are easy to overlook:
http://www.ootnaboot.scot/winter2008-9/20090131Liathach_Panorama.jpg
- the odd flat-topped Beinn a'Chearcaill, again a little North of Torridon:
http://www.ootnaboot.scot/autumn2010/20100925Beinn_a_Chearcaill_Summit.jpg
- Beinn na-h-Eaglaise:
http://www.ootnaboot.scot/autumn2013/20130908Beinn_na-h-Eaglaise.jpg
- And even the quick and easy An Ruadh Mheallan, West of Beinn Alligin, dwarfed by its neighbour but with good views and steep cliffs on its North side:
http://www.ootnaboot.scot/scrapbook/20110901An_Ruadh_Mheallan.jpg