Re: Low muscle tone
findingdx, my son also suffers from mild hyptonia (low muscle tone). My son hasn't yet got a diagnosis, but I'm pretty sure it'll be a form of Autism. I went for almost 2 years without realising anything was wrong, looking back now all the warning signs were there, but at the time I was a new mother and just had no idea.
When my son was a baby it took him a long time to be able to hold his head up on his own, when being picked up by his underarms he'd often almost slip out of your hands as instead of his arms holding their place they'd just slide up, he couldn't crawl properly or sit up on his own until after he was 1 and didn't walk until he was 20 months old.
He is also very double jointed which is a sign of low muscle tone also, his joints seem to hyper extend (they seem to move in both directions).
He is 4 now and to look at him I don't think you can tell, it's not really a physically obvious thing. The only obvious things are that he tired easily now and can't walk long distances, when you pick him up he is often floppy and he slouches down in his seats and the aforementioned double jointedness.
For me I don't think diet had anyhting to do with it because this was present from birth and a baby's only dietary intake that early is milk. Like others have posted, I've been told it's just a symptom of several different disorders.. now I just have to wait and see which one they decide it is.
Good luck with everything.