Nicole Richie's daughter cried "tears of joy" at her birthday party.

Harlow, Nicole's first child with husband Joel Madden, turned four-years-old last week.

Nicole and Joel threw a lavish Disney's Toy Story themed party to celebrate their daughter's milestone.

Harlow seemed flushed with emotion at the bash.

"Harlow started crying when everyone sang happy birthday and Joel said she was crying tears of joy," an onlooker told Us Weekly magazine.

Harlow's party was attended by 35 children. The tykes were entertained by their favourite characters from the film, including Woody, Jessie and Buzz Lightyear.

Partygoers were fed pizza, juice and a sugar-free confection produced by baker to the stars Cake Diva.

Attendees seemed to be having an excellent time.

"Everyone had a blast and Joel and Nicole said it was their best kids party yet," another insider detailed.

Gavin Rossdale, Sara Gilbert, Rachel Zoe and Tobey Maguire's wife Jen Meyer brought themselves and their children along to the bash.

Nicole and Joel also have two-year-old son Sparrow together.