Aggression on the lead

Question
Hi, I am hoping you can help me.  I have a two year old English working Cocker Spaniel (speyed bitch) who used to walk really nicely on the lead, until recently.  We were out for a walk a few weeks ago and a toddler ran out of a side entrance which startled my dog and my dog snapped at the toddler, but I pulled her away before any harm was done.  The toddlers Father started shouting at me and the dog, saying that she was vicious and should be muzzled.  That was the first time anything like this had happened and since then I am so scared that she will bite anyone that approaches, I will only walk her very early in the morning or late at night in case we encounter any children. When we do happen across anyone I tend to cross the road to avoid any problems.  Do you think I should have a muzzle fitted?  I have heard that this type of aggression is caused by the dogs being over protective and is difficult to break.  What would you advise?  Thank you for your time.  

Answer
I imagine (not seeing her etc) that the initial incident was due to the surprise of the child suddenly appearing.  Since then, your nervousness on lead is probably making the situation more stressful for both of you.  Always make sure when you walk a dog on lead that you are very aware of the surroundings - so that you notice something first.  Once you see something (in this case a child) force yourself to relax and your dog may not even notice.  If you clicker train then I would click and treat some basic behaviors (sit, down) to get her attentions.  Then click and treat a "normal" behavior or ignoring the child.  Basically treat like crazy any appropriate behavior.  Make sure not to avoid children (although you can do this on the opposite side of the street at first) since avoiding them will only leave a potential negative memory which will be harder to deal with later.  
Don't worry about a muzzle and it really doesn't sound like she is being protective.  Just watch her body language, click and treat appropriate behavior, calm yourself so she doesn't get that stress through the lead and react proactively!

I hope this helps.  Since it was a first time incident, it sounds like something you could fix with a little work.

ps - I would have told the guy to leash his child since you could have been a car!