"One raindrop, and she'd melt," joked her playful dad.
Despite the uncharacteristically bad weather, the opening was a meaningful accomplishment for Richie and Madden, who pledged to raise $35,000 to build the playground in September 2008 through the Richie-Madden Children's Foundation.
"When we first started coming here, there were no kids outside," says Richie. "To see the place come to life and have a place to come outside and be kids, and have their imaginations run wild, it's really awesome."
Along with Benji Madden, the couple announced a partnership with 7-11's Coffee Cup with a Cause, in which they'll donate proceeds from coffee cups designed by Richie to the Richie-Madden Children's Foundation between now and March 15, with a guaranteed minimum donation of $250,000.
"We're humbled to be a part of it," says Joel. "Today is a big day for our family."
Back at the Richie-Madden household, each day is a big day. "Harlow is happy to be a big sister and every day is something new," he says. "Sparrow is a little dude now. He's laughing, picking things up, and trying to talk."
What's more, quipped Richie, "Benji just started talking!"