I went and took a closer look (it's mostly been Mom's project lately, she was always more into houseplants), and they've actually grown more than that makes it sound. We have *four* cactus plantpots on the kitchen windowsills, each with several sprouts (though only one with anything that could be called an "arm"; the other sprouts are more separate than that).

(I think each tiny cactus plantpot originally had two tiny cacti in it, all of whom survived and ended up growing big enough to need their own pots.)