Talk to your veterinarian to get information about what is currently going around among dogs in your area.
It is best if you do not expose a puppy until after final vaccinations have had time to take effect--4-5 months of age. But they need socialization before that.
I would avoid a park or any other grassy area used by other dogs. For walks, remember that in some areas and seasons, daytime sunshine can make pavement hot enough to burn the pads off a dog's feet--very bad. But pavement not used by other dogs is a pretty good place to walk your pups if you watch the temperature.
I wouldn't take them into a pet store, either. A puppy training class that has NOT had any sick dogs at that location might be an option.
If your pups get tired, stressed, or otherwise in any condition that might lower their resistance; keep them especially private until they are well again.
Take the pups out separately and crate them separately. Pups kept together too much will become overly dependent on each other, and this is not healthy for them either emotionally or physically. They need to be raised and trained as individuals. Time together, but not left together all the time when they are pups.
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Kathy Diamond Davis, author, "Therapy Dogs: Training Your Dog to Reach Others," 2nd edition, and the free Canine Behavior Series articles at http://www.veterinarypartner.com/Content.plx?P=SRC&S=1&SourceID=47