Thank you all for your reply's. It has been helpful.
I have never owned a dog before so all of this from the start was a big learning for me/husband. Zutti has been use to children of all ages since we got him as a pup. My niece who is now 7, use to play with him for hours, and roll on the floor with him and cuddle him (which she can't do anymore) The first incident happend when my husband was working away in America (he did a lot when Zutti was a pup - probably most of the first 9 Months) my sister was staying over with my Nephew & Neice, they were sat on the couch and my sister was sat on the chair and l sat on the floor near Zutti, my sister cooked tea and l sat on the floor eating it, l gave Zutti a Big Bonio, which he was eating near me, then my niece wanted to come and sit next to me and give me a cuddle. She gave over, and he started to show his teeth, so l told Bethany to go and sit back down which she did. I finished eating, then she came to sit next to me, Zutti then punced on her and push her over. I was so upset l didn't know what to do, l shouted at him, then threw him into the kitchen and left him. Later on that night, l let him come back in and Bethany was wary then, she sat next to her mum, Zutti came in and sniffed her, then jumped onto the couch with me (he's not allowed on the couch anymore - which is better for all of us, especially with those mucky paws) my newphew asked to stroke him, which Zutti was fine with, then Bethany asked if she could and because he was ok with my nephew l thought he would be ok - Big mistake - he did it again and snapped! I know this was because he was with me and on the couch...
The only other times he's done this is when he's been on the couch and my niece went up to him from the floor to stroke - Snpped again! then with my neighbour's child, Zutti went to curl on the floor near my husband and within seconds she went down to him to stroke! I think we can see the pattern of this happening, but it still worries me.
I now ask all children to not approach him, unless they come to them, l have no bones/chews etc... around for him until they have gone to bed or he's outside.. But he tends to bring in things like sticks/toys, then plays with them on his own near the children, then if they move or get up he get's very protective of them - this is something l can't understand why he does that.
After some of your advice l took him to the vets on Friday to have hime checked over, she has reccomended having his castrated,
and has given me details of a Behaviourist.
My Newphew and Neice stayed on Friday night, they know the rules with him, and he was ok with them, and we took him for a walk on Saturday l let them both walk him, and he seemed ok, but l still need to keep an eye on him. I want to get this problem sorted with him soon as we are trying for a baby, so he needs to be prepared for all this to come.