Agree with Dave - most dogs will 'get it' after a yelp or two, and it's important that you let them
get it rather than forcing a separation (at least as long as a separation isn't necessary). Dogs instinctively pay attention to the yelp, and they generally learn pretty quickly how to limit their play based on their playmate's size and strength if left to their own devices.
When we brought Pepper home a little over a month ago, he weighed just over 2 lbs. Our older hav Cey is 2 years old and he weighs somewhere between 10 and 11 pounds, and he hadn't had much experience playing with dogs that much smaller than him (most dogs he meets are bigger, of course!). We supervised them closely at first of course, but despite the supervision Cey unintentionally sort of ran over Pepper twice while trying to play with him, causing Pepper to yelp. For the rest of that first night, Pepper was then deathly afraid of Cey and yelped like he was being killed if Cey acted like he wanted to play, even when Cey was a couple feet away. It took Cey some time to adjust, and rather than risk hurting Pepper again, Cey spent the next couple of days completely avoiding Pepper, even when Pepper wanted to play. Eventually, Cey started playing with Pepper again, but extremely
gently and carefully. Now, they spend hours each day wrestling and playing, and Cey has adjusted his playing with Pepper's growing size and always jumps back if Pepper makes the slightest yelping sound.
So yea, given a yelp or yip or two I really wouldn't worry about it, especially if you were right there to help out if it did in fact get out of hand.