I have been whistling in turkeys with poults for many years, decades in fact. It works.
When I see a hen with poults through the summer and early fall I will stop, put the windows down and start whistling the kee-kee run. The hens will almost always start calling back and usually even the poults start calling back as well. Frequently I will have a hen come in close and start showing her fan so the lost poult will be able to see her. I few years ago I had a hen so worked up she flew up on a tree limb about fifteen feet from my open truck window to see if she could see and call the poult to her that seemed to be lost inside my vehicle.
The one thing I would caution against though is doing it when the poults are young and it is raining or the grass is wet. During those wet periods you shouldn't do anything that delays or interferes with the hen and poults getting back together, so she can brood them, as quickly as possible.