Ashlee: Jessica Simpson “Is Happy” With Eric Johnson

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Ashlee Simpson-Wentz approves of big sis Jessica's new football beau, Eric Johnson.

"She is happy, so we are all really happy," Ashlee, 25, told at the Neil Lane/Kay Jewelers party at Drai's Hollywood Thursday night.

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"Her happiness is the most important thing to me," continued Ashlee, who was part of the group that flew to Italy to celebrate Jessica's 30th birthday earlier this month.

Ashlee says Jessica — who began dating her still-married guy about six weeks ago — isn't talking about having kids of her own.

VIDEO: Jess loses it while praying with a monk at a Buddhist temple

"She does love being an aunt though. She is a great aunt," said Ashlee, who welcomed son Bronx Mowgli with husband Pete Wentz in November 2008. "Yesterday he was over at her house calling her 'Jess' [and then saying] 'ica' a few minutes later. It was really cute."

Ashlee, on the other hand, "definitely" wants to expand her brood.

"We would love to have a big family," she tells Us. As for how many kids she wants, she said, "You can never plan something like that."

Bronx is growing up quickly. "Every day is like a milestone, I swear. It is the best thing," said Ashlee. "I mean, being a mother, taking the time that I have taken off just to be with him has really been incredible. Every day he is learning something new and growing. It is fantastic. I feel very fortunate."

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How do they spend time together? "We paint. He loves the water hose outside. That is always exciting, especially because it is extremely hot outside right now. We write on the walls with chalkboard and chalk," said Ashlee. "It is fun and it keeps you active because every day you're thinking, 'What are we going to do?' Even if it's just dancing in place. He is really cute. He is really becoming his own little man."

Even though dad is in the band Fall Out Boy, Ashlee is the one who sings to him. "He knows mama's voice because I sing for him all the time and we sing together," she said. "He knows the Elmo song; he sings that in the car, which is really cute."

His favorite music: "He loves Jay-Z. He says, 'Jay-Z ma ma.' So we do the ones without the swear words."

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