The 42-year-old actress admits that while they've taken road trips around California, she's not taken her 11-year-old offspring on a full vacation abroad for several years.
So when OK! magazine offered to fly them to Maui for a photo shoot, Madsen jumped at the chance - and learned how to relax.
She says, "I haven't been on a vacation with him since he was two years old, and he's 11 now.
"I don't know what I was thinking, but I just never took the time. Every Fourth of July we would drive up to Northern California, but that's the only sort of getaway that I would do. I would go up to Santa Barbara wine country for a couple of days.
"But I haven't actually got on a plane and gone somewhere just for fun and relaxation. It really took me three days in Hawaii to decompress from all the pressures of the city. I was in the spa, the end of the third day, and I sort of went, 'Ah, now I get it, this is what you're supposed to feel like on a vacation!'"
Madsen and her son made the most of their trip by engaging in a host of activities together, including snorkeelling and surfing.