The 48-year-old singer and actress shared a photo of 9-year-old daughter Emme and son Max from their first day back to school Thursday.
"So proud of my babies... #notbabiesanymore #4thgrade #love," she captioned the picture on Instagram.
The snapshot shows Emme and Max smiling as they pose in their school uniforms. Both kids wore white shirts and a blazer featuring their school's crest, with Emme in a pleated skirt and Max in khaki slacks.
Lopez shares her twins with ex-husband Marc Anthony, from whom she split in 2011 after seven years of marriage.
She has since started dating Alex Rodriguez, and spent the weekend celebrating Warren Buffett's birthday with the former New York Yankees player.
"Out here in Omaha having a laugh with this amazing guy... #WarrenBuffett #wisdom #fundamentals #keepitsimple #dowhatyoulovewithpeopleyoulove," the singer captioned a photo Friday with Rodriguez and Buffett.
Rodriguez himself shares two daughters, 12-year-old Natasha and 9-year-old Ella, with ex-wife Cynthia Scurtis.
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He and Lopez often combine their children for family events, including a cozy day at home in July.
"[Their kids have] really bonded and become good friends," a source told E! News in April. "A-Rod's older daughter, Natasha, is like a big sister to J. Lo's twins."
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