I have two big dogs (50 lbs & 70 lbs) and two little dogs (22 lbs & 8.5 lbs) The bigger girls have learned to play with the two little ones very nicely. When it's time to gnaw and gnash at each other (a lot of posturing) the big girls lay on the floor so they put the little dogs at an even advantage. There have never been any nips or yelps from this playing.

From my point of view, it's been a positive experience in socialization for all of them. Shows that big dogs can be gentle giants when necessary.

When Molly (8.5 lbs) went to puppy class, she didn't notice the difference in size because of the way her brother (22 lbs) and sisters (50 lbs & 70 lbs) play. I pretty sure she thinks she's a rottweiler - fearless and courageous to the max!