Clinicians often ask how they should write goals for preschoolers. The challenge is that the bulk of the therapy work is done with, by, and for the parents. Unfortunately, we can't write IEP goals for parents (as much as we might like to). So, we have to write the goals about what the child will do in the context of what the parent or clinician is doing. This shift in focus allows us to continue to do what we do in therapy with little kids while still writing well-formed goals.
Of course, the specific goals that you write will depend upon what you recommend for therapy. If you're focusing on less-direct therapy (as is common in the earlier stages of therapy), then you can write goals about how the child will react when the parents make modifications to the environment. For example, "the child will demonstrate a reduction in speech disfluencies when parent (or clinician) does XYZ"—note that the focus is on what the child does even though the context that we manipulate is the parents or clinician. (XYZ might be various types of environmental modifications, such as reducing time pressures.) This kind of goal becomes measurable when you specify what situation the parent will do XYZ in, how often they’ll do it, etc. (And, of course, you’ll need to add in whatever other specifications your district requires, such as over what time period or how many consecutive days, etc.)
For more-direct aspects of therapy, then it is easier, because you're focusing on what the child does. There are two key aspects of more-direct therapy that I focus on: the child's speech (with goals related to the child learning about the speech mechanism, how speaking works, what stuttering is, and how to make changes in speech to minimize stuttering) and the child's communication attitudes (with goals related to the child demonstrating acceptance of stuttering by talking about stuttering openly with the parent/clinician/others...). Again, the specific goals will depend upon what you think this particular child needs (though I think that all children benefit from the attitudinal work).
An important thing to remember is that young children are not likely to generalize speech management strategies because of their age and abilities, and gaining fluency in the clinic doesn't really help them out in the real world. So, be sure that you start with a healthy dose of education and awareness (even in the little ones) to guide them.
You can find lots of examples of goals for preschool children who stutter in Early Childhood Stuttering Therapy: A Practical Guide—including our exclusive “goal frame” that makes it easy to simply drop in the key aspects of your goal while maintaining language that is appropriate for your school-district.