My puppy comes accross as aggressive.?

Well, thats what people think when in fact he is absolutely harmless and really affectionate. When children approach he barks and runs to me. When hes playing in the frontgarden with our younger pug (hes a pug too, 7 months now) a neighbour will come up to the gate asking if they can pet them and i say yes but my pug just barks at them. i have to go up to the 'stranger' with him and hell have a bark but then hell approach them and wag his tail and lick their hands. So, really he needs to be given a chance but when its children they dont understand. I tell them he wont bite but he bark at them and runs to them. (his tail will wag if he gets close enough but theyll sort of lean forward with their hand out - which ive heard leaning over is seen as threatening to a dog) Then he will run back to me and bark. Ive tried getting him used to children. One of my mums friends came round with her child. Milo barked at him. But it was a young child it got the vacuum cleaner and started swinging it around and dragging it around the house and nobody told him to stop. not even the childs parent. (Im only 16 myself, id rather not be shouted at for telling the kid to stop. Its bound to happen) Now my pug is even more scared of children and has become frightened of vacuums again. JUST after i had gotten him over his fear of them. He was absolutely fine with vacuums and now he cant stand them. What can i do?! He goes to cles but when hes at training cles he ignores the children completely but when were out and about he gets frightened. He had never seen children until he came to live with me (at 4 months old). His breeders were quite old and he didnt get alot of socialisation.