The guest of honour dressed up as her favourite Disney princess, Snow White, as she was joined for a happy snap with a lookalike entertainer,New Era Hats Cheap .
Red apple cupcakes were in keeping with the theme, while the family's pool was filled with large colourful balloons which were weighted down to give the appearance that they were floating on water.
'Party time!! Happy 5th birthday my princess Anja!!' the doting mom wrote to accompany the fun pics, adding, 'Today is all about my princess Anja!!!'
Despite her hurried look, Alessandra still sported perfectly manicured bright red nails and had also accessorised with different necklaces and bracelets, giving her look a rather bohemian edge.
She appeared relieved as she approached her car, no doubt keen to unload the heavy box and get home to finish setting up for the party.
With any luck, fiancé Jamie Mazur was busy pitching in as he held down the fort caring for Anja and the couple's son, Noah, 15 months, while Alessandra nipped out.
Posting several photos of the festivities to her Instagram account during the day, the couple's home was decorated with colourful balloons and streamers for the pretty princess themed do.
The stunning brunette wore a pink and peach tie-dye halterneck maxi-dress, cheap new era cap, which had a sexy slit on either side showing off the leggy model's toned and tanned legs.
In keeping with the low-key look, the model opted for a pair of cream flip-flops and covered her eyes with dark brown tinted sunglasses.
She clutched a brown Chloé handbag in one arm while cradling the box of champagne with the other.
The 32-year-old made sure she had everything she needed to enjoy the celebration as she popped out to Whole Foods in Santa Monica for some last-minute purchases.
It looked as though the Victoria's Secret model had stepped out in a bit of a rush, as she was completely make-up free and brandishing a noticeable blemish on her cheek.
But being the successful supermodel she is, Alessandra still managed to look amazing, and even had her long tresses styled in soft curls.
The lucky little lady officially turned five on August 24, but her doting parents weren't content with just one day of festivities to mark the milestone.
And being the Labor Day holiday in the US, what better opportunity to gather the family's nearest and dearest for some fun in the Californian sun.
'Waking up to an amazing party and holiday weekend...' the supermodel tweeted earlier that day.
Like most of her fellow Brazilians, she knows how to have a good time.
From partying in Ibiza to throwing lavish parties for her children's birthdays, model Alessandra Ambrosio certainly knows how to kick back and relax.
And on Saturday it was no different, as the mom-of-two dashed out for some extra bubbly for her adult guests ahead of daughter Anja's lavish princess-themed fifth birthday celebration.
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