Help! My normally lovely dog is snapping at children

I have two Golden retrievers, a neutered 22-month-old boy, Teddy and nine-month-old Lola. Lola is a total darling and is super friendly to everyone. I would have said the same of Teddy, until two months ago when we had new neighbours move in. They are friends of ours and their children play at our house with our children. 
I'm writing this as, for the third time Teddy has growled at or snapped at the children. Each of the three children have now had a bad reaction from him and I'm stunned. Teddy is a very calm dog, typically soft mouthed, well trained and obedient. He isn't a push-over submissive dog but he is not aggressive. 
The first reaction happened when Lola was being fussed by the children and the 10 year old girl came over to Teddy to give him a stroke. Teddy growled at her. The second time was when the seven year old boy petted him. Teddy made a snap at him. I thought this may be because Teddy and Lola had been play fighting and the lad moved suddenly towards Teddy, when the 'game' had just finished. The third time was when I had hold of Teddy's collar and the seven year old girl stroked his head as she walked past. Teddy snapped at her hand. My own children are 15, 13 and 10 so the dogs are used to children in the house.
I'm really perplexed as to why this is happening and I'm really disappointed too. Teddy barks at the door bell when the children arrive but scrambles to greet them when they get in. I can tell the children to ignore Teddy and I can keep him away from them but I'd really like to know why he is reactig like this. He's not protective over Lola - is he protective over me? I have been standing by his side each time this has happened and he is a mummy's boy.
Any ideas?
Thanks
Sam Young


Karen Wild, Canine Behaviour Counsellor, says...
It certainly sounds as if Teddy is not comfortable with the children approaching and petting him. The safest option is for you to immediately seek professional help and at present your suggestion is correct, do not allow the children to approach or pet Teddy for now. Ask your vet for referral to a behaviour professional such as an APBC member www.apbc.org.uk who will be able to help you teach Teddy to learn some safer habits. A growl is a clear warning that a dog is not happy with a situation and the more 'history' a dog has of the same reactions the more likely they are to repeat the same behaviour, escalating it each time (hence the snapping behaviour you witnessed on the third occasion). I can understand your feelings as it can come as a real shock to see your beloved dog behaving in this way. Try to think of it in terms of Teddy communicating his unease in the only way he knows how. If these warnings go unheeded, he has no option but to take it a stage further each time. This does not mean he should be branded as a 'nasty' dog - it sounds like he sees some things as a threat and would rather keep his distance. Owners often tell me their dog is not 'aggressive' but truly, most dogs that bite are often out of their comfort zone but are lovely pets the rest of the time. His reaction in this case could be for many reasons so do take that first step - contact an accredited behaviourist who will help you - and Teddy - to regain that level of confidence again.