ET's Keltie Knight spoke with the journalist and philanthropist at the 3rd Annual Best Buddies Mother's Day Celebration hosted by Hublot at La Villa Contenta in Malibu, California, on Saturday, where she was supported by her children, including bride-to-be Katherine Schwarzenegger.
"[Wedding planning is] fun," she gushed of Schwarzenegger's upcoming nuptials to Chris Pratt. "I think it's always great to celebrate love. It's the most important thing in the world. You learn unconditional love ideally from your mother and then if you find it in your life, you're blessed."
Shriver said she hasn't yet decided what she'll be wearing to Schwarzenegger and Pratt's wedding, but it's clear that if there's one thing she's certain about, it's that Pratt's the right guy for her daughter. "I think he's great," she shared.
"Chris is a great guy," echoed Shriver's brother, Anthony. "Actually, I had dinner with him last night. They seem so happy and so in love."
A source, meanwhile, tells ET: "Katherine and Chris are enjoying the planning of their wedding. The couple plans to have a star-studded event filled with family and some of the biggest celebrities in Hollywood. Katherine and Chris want the wedding to also be fun, as the couple always has a good time together. Katherine has been in charge of most of the wedding planning as Chris had been promoting his movie, but he does give suggestions and helps when he can."
The love birds, who announced their engagement in January, still have a while to go before their wedding. For now, Shriver is focusing on Mother's Day, which she told ET she would be spending with her kids: Katherine, 29, Christina, 27, Patrick, 25 and Christopher, 21.
"Hanging with my kids, loving on them, having them laugh with me, sit with me, tell stories with me [is on the agenda]," she said. "That's it."
"It's a marathon," Shriver said of motherhood. "My mother always told my brothers and myself, and I say this over and over to my kids -- your family is the source of your strength, the source of your stability and the source of your joy."
The mother of four said the value of giving back is also something she's tried to instill in her children. She's been a global ambassador for Best Buddies International for years; the organization -- which is dedicated to ending the social, physical and economic isolation of the 200 million people with intellectual and developmental disabilities -- is celebrating its 30th anniversary.
"I think it's important to try to raise your kids [to care about giving back]," Shriver expressed. "And also, I think it makes your life meaningful. It gives you a sense of purpose in your life and a sense of meaning and I think that's what helps you get up everyday and go out and face the world as if you have a vision and a mission and that it's not about you."
"I think celebrating remarkable women, remarkable mothers [is important]. So many mothers that have special needs kids that are really working tirelessly to raise their children and give them access to all the same things that everyone else has. So, to be here to celebrate remarkable mothers is a great gift," she said.
For more information on how you can help make a difference in the lives of people with intellectual and developmental disabilities, please visit bestbuddies.org.