now growling only after hes been fixed

Question
We adobted a 11 month old rottweiler about a month ago he was gentle and playful until we got him fixed now hes growling at us if we go to close to his face or when he has one of his bones he growled and snaped at my husband twice we have children and i cant be worried anything is going to happen we love him to death whats going on please help

Answer
What you refer to is known as "food aggression", or "resource guarding" (some dogs guard food, but others guard space, people, toys, etc.) and is very dangerous if you do not address it, but generally has nothing to do with the dog being neutered or not, and is probably coincidental (although pain from an incision can make a dog testy, and this is one way to take it out on the nearest human).  For now, please do not give him food or bones when your children are about, and do not try to take such things away from him.  "Testing" the dog makes it worse.
There is a book on this subject which can help you train him to relinquish his "special things" without being nasty about it.  It's by Jean Donaldson, and it's called "Mine! A Guide to Resource Guarding in Dogs".  Available on Amazon.com I think.
Rotts can be socially dominant dogs, and they need consistent, sensible training, but that doesn't mean rough training.  I advise you to find a trainer who has experience with this breed, but does not use harsh methods, and sign up for class.  This is a good age to do that, and remind the dog that the humans are in control of the household. With dogs, leadership is often equated with who controls the resources...and training helps with that.  
If your kids are young, his behavior can be dangerous to them (picture a big dog going for the turkey wishbone that just fell under the table at the same time a little hand reaches for it - not a pretty sight).  So, do get a handle on this quickly.  Even dogs that are usually wonderful, happy companions can get themselves in serious trouble if they guard food or special items.  And, you have a large breed that is potentially very dangerous in this situation, just by virtue of the strength of his bite.