You should not leave your puppy alone with older dogs until it is four months old. Until they are four months old, puppies do not properly display submissiveness. In addition, they want to play! So they can end up pestering and annoying older dogs. Most older dogs will respond by growling or snapping at the puppy but they may also bite the puppy.

Photo from: http://www.flickr.com/photos/fpat/ / CC BY 2.0

Information from How to Raise a Puppy You Can Live With.