Adding music to iPod shuffle given as gift.

I just picked up four refurbished Apple iPod shuffles to give as Christmas gifts to my sister's children, ages 6 through 13. I'd like to personalize each iPod shuffle by purchasing and preloading a few songs that I know are special to each child. How can I do this with a single Mac? I also want them to be able to transfer the preloaded songs to their family PC.

I'll probably give each child an iTunes giftcard so they can further customize their gift. Any help is greatly appreciated.

Thanks,
Kelly