Help, Kitten Vomiting

Ok, so like two times already I woke up in the morning to find my cats running, playing, and exploring under my bed.
Thats great and all except for the BIG YELLOW VOMIT STAIN ON THE CARPET!!!
About 3 days ago I started feeding them Nutro Max kitten wet food, and one of them (i think one) started throwing it up.
So I switched to the KMR second step (the kasha-like food).
And today apparently he threw up.
Why could he or they be doing it?
They dont seem lethargic and play alot and sleep normally. (when one wakes up usually the other one wakes up).
Another problem though, Mischief hasn't pooped for a while - I think.
I found a poop in the litterbox today, but once again I dont know from who its from and Mischief's butt is as clean as a whistle.
Ive also noticed they are using their legs to scratch themselves alot and they lick themselves alot more than they did when they were younger.
They are about 6 weeks old.

Vomiting could be worms or overfeeding, or not feeding the proper food for young kittens. Vomiting is a concern for young kittens because they dehydrate so quickly-

Chaos threw up a little bit right now, and then afterwards just went on playing with Mischief! They're playing as we speak, pulling on cords, trying to climb bed sheets, jumping on each other, doing everything they would on a normal day.
I noticed they lick themselves alot though, maybe its hairballs?

Is the stain you are finding obviously thrown up food or is it clear, like stomach fluids? How often are you feeding them? As for licking themselves, have you checked for fleas? Switching foods back and forth as you are can cause digestive woes - if you are going to switch around, give it at least a week to 10 days before switching again.

~gf~

It was food, yellow liquid (the KMR second step powder that I mixed with KMR milk to give her the day before)
I feed them 3 times a day. Morning (7AM or 12PM) and then 3-5 PM and last 9-11 PM.
I tried giving Chaos (who threw up a little again recently) some water but wouldnt drink it.
I checked for fleas, there are no visible fleas, although I saw one a week or two ago, but they are not visible on their body, I dont see any bugs on them at all.
Chaos is sleeping now near the bed (she tried throwing up a bit again, but only saliva and water came out). She was gagging on it and moving her body up and down like an accordian.

Sounds like worms to me.

I would recommend a trip to the emergency vet. Yellow vomit is a possible sign of distemper. If this is the case (and I really, really hope it's not), then aggressive supportive care will be necessary and the sooner you start, the better.

Ok, woke up today everything seems fine.
No puking, no gagging, came back after school and no vomit stains.
They ate and are playing with each other on my foot.
Plus my friend got his kitten checked out and the vet said it didnt have anything and it was perfectly ok (i found my kittens with his)

Only because you friends kitten was healthy is not a good meter on wether the others are as well. They should be checked by a vet no matter what!

Ok she didnt throw up today, but she pooped.
The poop is light brown. This changed a couple of days ago, where when I first got them their poop was dark brown.
And Mischief isnt pooping for some reason. His buttocks doesnt appear dirty and there is no poop in the litterbox. Where does he excrete? He eats more than Chaos.

Could Chaos have distemper? She vomitted yesterday like 4 times but she was still playful and is playful now.
Theres no blood in her poop or anything, its light brown.
It says a symptom of Feline distemper could be seizures.
Im not sure but after they drink they kind of move their head in a weird way and make a weird sound, kind of like a cough. They do that after they eat too sometimes.
Is that normal?

If I were you....even if the kittens are not sick now, I would bring them in.... certain worms/ parasites can have dormate periods, or will only lay eggs for a certain ammount of time...or will die after a while......

have the vet check them out and have them dewormed as a precaution.......

Ok, but just to be safe is there any "out there" symtpoms of anything I should be looking out for? Other than the vomiting and not eating that day thats all I noticed.
That and the hiccups or coughs or whatever it is they let out after drinking/eating.
Oh um today Chaos was playing with Mischief and I think she was too agressive.
He was meowing and she was all over him and he couldnt even kick her back or whatever.

I am not really sure of what symptoms to be looking out for...cause I am not sure the diagnosis of the cat.....and I am sure if i mention all the syptoms that i can think of that may be noteworthy...i may be leaving out like 100 others...and that will be bad for the kittens......

maybe others can give better advice in the symptom department....but just remember as brilliant as the people on here are....they can not definitly diagnose anything without seeing your kits first......thats why i suggestd getting them to a vet.....

Its cool that you are trying to care for your cats and try to get a diagnosis, but dont let it end there.......its happened way too much on this site.... people come on thinking this site will cure thier cats, and thats not the case..............this is an advice only thread...........

my advice is a trip to the vet accompinied by a good deworming....but others might have more advice for you......

but please keep us updated..... ....and i know we would all love to see pics of your kits....

good luck