To parents with children in the Autistic Spectrum, how do you deal with a major anxiety meltdown?

All children on the spectrum are different so there are different ways of coping with them. If you can tell that the child is heading for a full blown meltdown the first thing to do if possible is to remove them from the situation and get them some where safe and quiet. They also tend to like their own space, my own daughter will not let me touch her until she is ready and that could be several hours later. If they are going to have a full meltdown then there is nothing you can do to stop it you just have to ensure they are safe and secure. At the moment I am pretty sure what triggers my daughters fears so I tend to avoid those situations. I am sure as your son grows you will learn when he is heading for a meltdown and what to do without even thinking about it. Do try different things with your son as what works one day will not work the next. I know with my child I can sometimes get it wrong and make the situation worse but then at other times I can do just the right thing. Just make sure your child feels safe and secure and that he can come to you with his fears.