They are not below average sized guys for sure. Not sure on weight, but height is readily available. Spain is considered a very small team, and they still had 4 dudes on their roster that were over 6'3"Just looking at the players, I'd say the average height and weight of WC players was below 6" and well below 200 lbs.
To show you the average height of selected teams...
Brazil averaged 5 feet 11 and a half inches and has 10 out of 23 over 6 foot with 3 over 6'3"
USA averaged 6 feet and one half inch and 15 out of 23 were over 6 foot with 5 players over 6'3"
Germany averaged 6 feet and one inch and 18 out of 23 were over 6 foot with 7 players over 6'3"
Spain averaged 5 feet 11 inches and 11 out of 23 were over 6 foot with 4 over 6'3"
Soccer is game that can be played on the ground or in the air, and only a handful of positions require raw strength so you can get world class players that are undersized, but as with other sports, its generally a big man's game when you talk about the general sizes of the players. Each of those average height numbers for the soccer teams is 2-3 inches taller than the average male in that country.