"A student is enrolled “at least half-time” if he or she is enrolled for at least half the full-time academic workload for the course of study the student is pursuing, as determined under the standards of the school where the student is enrolled." (Source). For purposes of the CSS Profile, you'll have two children enrolled at the same time for the upcoming academic year. It does not break it out in to "half-years." So you'd respond that you have two children enrolled.
Brian Boswell VP, Research & Development
This information does not constitute tax advice and is provided for informational purposes only. Please consult your tax advisor, financial advisor, local taxing authority, and/or plan provider or sponsor for more information.