Tiny creatures get a +2 AC bonus, a +2 bonus to attack rolls, a +8 bonus to Hide checks, and a -8 penalty to grapple checks. They can use Small weapons (like a short sword) in two hands and Tiny weapons (like a dagger) in one hand.
Armor for Tiny creatures has half the cost, half the armor bonus, and weighs 1/10 the normal weight. (PHB p105)
Tiny creatures have 1/2 the carrying capacity as a medium creature with the same STR score. (PHB p142)