One note: You can actually use a Human feat, Racial Heritage, to play the character as a halfling instead with access to all the same feats and traits.
That said, Halflings are really amazing at this job. I'm posting as such a character right now. There's a lot of ways to go about playing a helpful character based around Aid Another. I use a Halfling Fighter (Tactician) who will eventually take a single level splash into Monk (Maneuver Master); Cavaliers are a much more popular option, partly because your mount can ALSO use Aid Another, meaning even more attack or AC for your allies. Let me give you a few feat links. Feats are VERY important here.
Bodyguard - This feat, once you've got it and its prerequisites, will allow you to defend your allies easily. I think you can get this on your mount if you're a Cavalier, since it only requires Combat Reflexes, meaning your mount can ALSO be using Bodyguard on your allies... and on you. (I know you were already looking at this, but consider the ramifications of having it on your mount or animal companion if you get one.)
Swift Aid - This lets you use Aid Another once per round as a Swift Action as well.
Cautious Fighter, Blundering Defense, Crane Style - Get these feats if you can. You'll be boosting your allies' defense around you just by standing there looking pretty. Also grab 3 ranks in Acrobatics; it'll net you +1 AC when fighting defensively. Total this up: 6 AC when fighting defensively, 3 of it being given to your allies, and all this at only a -2 attack penalty.
If you want to get an animal companion to provide Aid Another bonuses as well, consider the next two feats: Nature Soul and Animal Ally. Two feats for an animal companion of your choice? Sure, why the Hell not? You can be any class you like to get this benefit.
Since you're not going to be optimizing for damage, you should probably pick up something to do when you're not throwing Aid Another around. I decided to specialize in Dirty Trick, but there are other maneuvers you could consider; and if you're a caster you could always cast spells or use a wand.
As far as traits go, Helpful is definitely nice, but I think that there's another trait (a campaign trait) that gives +1 Aid Another. Wait, here it is: Fools for Friends. That would give you +3 Aid Another, bringing you to +5 total.
This should be enough to get you started. As I said, there are LOTS of ways to do this.
EDIT: If you DO get a mount or animal companion... I strongly suggest the Wolf or Giant Chameleon. The Wolf gets Trip; need I say more? The Chameleon gets a climb speed. Climb speed. Small creatures can ride either of these into battle, too.