Worried about big dogs around my tiny pup?should I be?

Ok so my local park is fulllll of all dogs off lead,and also ALOT of dog walkers,with up to 10-15 dogs at a time of lead too.I took Coco here the other day and we had a nice time meeting lots of friendly dogs and puppy's that she "played" with (when I say play she pretty much observed and rolled around whilst watching them play) however I am wary about how to let other dogs approach her/how she approaches them.Is there a way anyone would go about introducing their puppy to dogs in the park?
We had a pleasant time until this lot arrived:

Dog walkers by sweetheart-roland, on Flickr

As they approached us I was unsure whether to pick Coco up,let her decide or just leave it.
Now on my first puppy class Coco was VERY scared by this young over enthusiastic King Charles spaniel she looked terrified and she tried to jump up to me,so I did pick her up,however the trainer then commented "Coco will learn everytime she is scared or doesn't like something she will think she can just jump up over to you and mummy will protect her"So as we passed these dogs I thought,"ok I'll just leave her"She wasn't acting scared or anything ...until they(the small matching dogs) approached her.
They both were sniffing both her ends at once and she was just frozen to the spot looking....VERY small(which I guess she is)Now at this point i thought ..."Ok she is a bit scared but their not hurting her etc and she seems to be dealing with it" then they decided to SWAT her with their paws..."arghhh I thought!My poor baby" and then she yelped and they backed off ... at this point the dog walkers came over and told them to "play gently" and they walked away.
My slightly paranoid 11 year old sister was panicking saying "omg omg molly their going to eat Coco"(lol?)Then the St.Bernard headed over,who was HUGE and the two twins followed,at this point I thought "screw it I'm picking her up and walking away",which we did.
Now I don't dislike big dogs at all I'm just very wary of something happening because of their difference in size and also the fact I am wary of bigger dogs due to being bitten by one once so I would NOT know what to do if say the bigger dog had been violent or something else.
So how have people on here....with smaller dogs(or just their puppies)dealt with meeting bigger dog's?Should I steer clear of dog walkers full stop?(I say this since I presume they will have less knowledge about their dog's then the owners)
On one side I don't want Coco to end up being over protected etc and thus being less able to play with bigger dogs but at the same time I really don't want to put her in danger...Did I react in the right way?
I guess today at puppy class I'm going to insure she meets and greets the huge German Shepard who is owned by the trainer and brought to classes to be a positive adult role model ...

Since you are wary of big dogs, you pup will probably sense this some. I would definitely ask people if their dogs are friendly and like small dogs/pups before you let them great. I'm always going on the side of caution.

This is definately something that small dog owners need to be vigilant about when they choose to take their small dogs to dog parks with large dogs you don't know. I have a 7-pound chihuahua, and we've only been to the dog park once or twice because I don't trust the other dogs (or their owners) who may be there. You never know if a big dog is going to see your little dog and think "PREY!" and go after her. It certainly can happen.

It's also true that if your little dog is scared of big dogs, it could make the big dogs more dangerous for her as well. If they think that she's starting a fight, they will be more inclined to fight with her. And if she sees that you are scared of the big dogs, she will be more scared and more inclined to want to fight them away.

In short, I would not take a puppy to a dog park, unless possibly it had a small dog section where she could play with dogs her own size. Even then it's a little bit of a crapshoot, even small dogs can be aggressive and cause serious damage. Instead, I'd suggest socializing your puppy with friends' dogs and other dogs that you know are good with small dogs. This will make you more comfortable, as you'll know there won't be a fight, and in turn it will make your puppy much more comfortable to see you comfortable.

Dog parks are not for every dog, and the problem is that even if YOUR dog is good at dog parks, there's no guarantee that every dog there will be good for dog parks. They can be very dangerous, and you should always be cautious taking your dog to a busy dog park.

Thanks guys for such good advice!
My trainer also made the point of saying that I should get her to concentrate on walking on the lead and not only going to the park to play with other dogs,and to use this to my advantage to train her for later on in life
cheers