You are not quite as big as other people, but that never slowed you down. You can't carry as much, but you are more agile. You get a +1 bonus to your Agility, but your carry weight is equal to 25 + (15 lbs. x Strength), instead of 25 + (25 lbs. x Strength). The extra stat point gained by this trait can be set on any other SPECIAL stat, like with Bruiser and Gifted.
Due to your small size, you have +1 Agility but your limbs are more easily crippled (25% extra limb damage).
J.E. Sawyer's Fallout RPG
You are smaller than average. It's hard for you to carry heavy loads, but it's easy to avoid the lumbering giants of the wasteland. -50 to carry weight, +2 to evade.
You are not as big as others of your race, but that never slowed you down. You can’t carry as much, but you are more agile. You get a +1 bonus to your Agility, but your carry weight is 50 pounds less than normal. Feralkins may not take this trait.
When combined with power armor, Small Frame can have some odd effects. Your intrinsic carry weight will be calculated using the 15 lb/point stat, while the "bonus" carry weight from the armor's Strength boost will be calculated with the standard 25 lb/point. This means that if you take the opportunity to improve your intrinsic Strength, your carry weight will decrease by 10 lb.