I have a long skinny baby too, 4months and 13lbs 15oz. I'm not too concerned as the family is filled with long skinny people
but the doc wasn't happy that DS has dropped from 85th to 20th percentile. My mother was always suspicious of his birth weight though, she figures they mis-weighed him and he was actually lighter than they say. We'll see what 6 months brings us. I do know that he's a lazy nurser so if he continues to drop then I guess I'll be concerned a little.
And crawling! OMG!!!!!