And it looked like so much fun!
It was especially great to see Brit's niece Maddie looking so healthy and happy! To think just a month ago she was so severely ill and nobody was sure of her condition! Go, Maddie!
Also along for the fun were the 35-year-old pop star's mom Lynne, sister Jamie Lynn, sons Sean Preston and Jayden James, niece Lexi, and Jamie Lynn's husband Jamie Watson. The only people missing were Brit's dad and brother!
The Make Me singer signed a few autographs and posed for some selfies before they all headed off to go on some rides and enjoy some seriously delicious-looking ice cream floats and cake.
Check out more pics of the fun in the gallery (above)!
And also make sure to watch some clips from the day (below)!