Jennifer Garner's son no longer thinks she's cool.

The 46-year-old actress threw a 'How To Train Your Dragon'-themed seventh birthday party for her youngest child Samuel - who she has with ex-husband Ben Affleck - and got into the spirit of the celebrations by dressing up as Astrid from the animated movie, complete with blue and orange face paint, a fur shawl and boots, arm sleeves and a pointy, leather skirt, but the youngster wasn't very impressed.

The former 'Alias' star shared a photo of herself presenting her son with his chocolate birthday cake and captioned the Instagram post: ''Well, guess what. It turns out 7 is the age my kid stops thinking it's cool when I dress up for the party. #youngestchild #firsteyeroll #anyoneneedanAstrid [facepalm, laughing, grandma emojis] (sic)''

But while Samuel wasn't impressed, America Ferrera, who voices Astrid, took to her own Instagram account to praise the 'Camping' actress for her efforts.

She shared Jennifer's original post on her Instagram Story and wrote over the top: ''Ahhhh!!!! Yeeeeessss!!! AMAZING @jennifer.garner as ASTRID!! (sic)''

Jennifer also has daughters Violet, 13, and Seraphina, 10, with Ben and the 46-year-old actor recently admitted the girls think he's an embarrassing dad.

He said: ''[For] my oldest daughter, I'm already embarrassing, you know what I mean?

''I'm like, 'How can I be embarrassing? I'm Batman. That embarrasses you?' She's like, 'Dad, pick me up down the street.''

Ben brought his kids onto the set of 'Justice League' and the girls were particularly taken with Gal Gadot as Wonder Woman.

He said: ''The girls were into Wonder Woman.

''I like to think they were into Batman a little, but my girls [were] definitely into Wonder Woman.''

But young Samuel was overwhelmed when he saw Ezra Miller as The Flash and ''got really shy'' when he saw the actor in full costume.

Ben recalled: ''I was like, 'That's the real Flash.' And he looked like he saw Jesus Christ.

''I was like, 'Yup, that's him. That's the one, the real Flash.'''