I think you're doing a great job. I have a 7 year old with a mild stutter and other speech impediments. My SLP friend, who is very experienced in stuttering, told me that at the toddler age, the best thing you can do is... nothing. Like you're already doing, let them talk, finish their sentences, and don't bring attention to it. If they start to be frustrated by it, or it has gone on for a prolonged period of time (around a year), then therapy might be helpful. Fortunately, most children who stutter do grow out of it. I really haven't picked up on my son's stutter much these days.