To flesh that out a bit I guess...
My son was a very picky eater, right out of the womb. He would only eat on one side, being held in a specific way. Often he would wake up crying from hunger, but wouldn't stop crying long enough to start feeding. After feeding, typically took 30-60 minutes of rocking before he would stop crying and go to sleep again. Later on, this developed into just general trouble in sleeping. He didn't sleep through the night until he was 3 years old. I'm not kidding. He was also very compulsive. ie: He would sometimes throw his soother out of the crib for some reason, and then start crying for it. We resorted to putting him to bed with a "spare" soother. Eventually, he wanted both soothers simultaneously, one in his mouth, one in his hand. Then that wasn't enough, and he wanted 3 soothers... the only solution to this was cold-turkey, no soothers. 1 week of hell, but then he got over that. It would be too long to go into all the details, but sleep was a big problem. He just did not want to sleep.
Now, I believe because of the lack of sleep, and continued poor eating, he's very small. He started out 25th percentile, and has fallen below 5th percentile. We don't really know where he is because the charts don't show lines below 5. He only gained 5 lbs between his 2nd and 4th birthday. Behaviourally... we've had some issues. He's compulsive and impulsive. Things have to be just a certain way or he flips out. He has tantrums almost every night before his bath, hits my wife, etc. He's in kindergarten now and has gotten in trouble for hitting other kids. For eating, the doctors insist that we only feed him good food, stick with it, and he won't starve himself. Well, he does. He's skin and bones. He's been sick pretty often this winter.
The flipside of it, he's *wickidly* smart. Never ceases to amaze us. At 4, he's fully bilingual english and french. He recognizes brands, and branding, whether it's Land Rover badge, Kraft, Bass Pro Shops... he knows the make and model of a surprising number of cars, and even understands design "language". He knows what a Hummer is, whether it's an H1, H2, or H3. The first time he saw a new Range Rover, he knew it was a Land Rover. He's been doing 48 piece puzzles since he was 3, and now tackles 100 pieces, by himself.
Don't get me wrong, he's a good kid. We've worked through a lot of his issues, it's just been a huge struggle. He sleeps pretty well now, and we are getting his behaviour under control. The only thing we really struggle with still is eating.
Our daughter eats and sleeps so well, she's shot up to 95th percentile at 3 months. Nobody in our family is that big. She's 15 lbs, and our son is 4 years old and he's 30. Unbelievable. She's also avoided every illness my son and us got this winter.