Bear in mind that your lowbies can be standing pretty far away and still get experience. When you're clearing an instance and your lowbies are aggro magnets, simply leave them in one spot and clear ahead with your main. Then move the lowbies forward when the area is safe. You might not be able to leave them very far behind in Stratholme, due to the Eyes of Naxxramas and the spawned skeletons (if you are doing live side). But you can clear it and avoid having to spend too much time worrying about them.

If I remember correctly, the skeletons that spawn as you clear live side always spawn after certain groups are cleared (or after you pass a certain spot). So you will be able to figure out when they're about to arrive and deal with them after one or two trips. Just remember to soulstone a rezzer.

I think my boosting route with my group was quest to level 8, then RFC from 8-14, SFK from 14-20, RFK from 20-24, SM from 24-37, RFD from 37-38, Uldaman from 38-45, ST from 45-48, Scholomance/Strath/DM from 48-60. Then after running HFR without boosting from 60-62, I have PLed them to 66 via clearing Outland instances once or twice. Right now I'm running them through quests in Nagrand which is slow but will get them some faction and gear upgrades (some of them are still using gear from Uldaman!). Then again I do not particularly look for the most efficient and quick method for leveling them and my boosting path was very much trial-and-error.