You never know. My cousin (who was not very big at the time but is now) had a really large baby who had lots of developmental delay issues probably for two inter-related reasons. One was he was missing a fairly large chunk of one side of his brain and two he was so big it took a lot for him to move. He didn't walk until some ridiculously late age, like 2 years old.
Any way, he's a about 10 or 11 now and pretty skinny and a good BMX rider.