For our groups first D&D excursion in 20 years, I converted Coppernight's Hold - which was in the 4e Dungeon Delve book - 3 small fights... and the DDI added another 4 in Dungeon Magazine to that. All total it was 7 fights and a little bit of role playing with NPCs between encounters. It also has a skill challenge for the players if you wanted to run it and do a puzzling play for the kids. They're 1st level fights, so the combat isn't overly involved and I thought it worked as a good introduction to the metrics and the idea of combat. It was very straightforward backstory and a single in and out mission. Or, if you have access to the Dungeon Delve book and/or DDI, both are full of small adventures for all levels - you just have to convert them. If you don't have access but your PC has Adobe.... there's always a way... PM me.