So is Sara just behave like a happy kiddo or she is being a yuri?
I think for Ark is yes.

Ark Yuri?

The kiddies found a new toy~

Welp, we've discovered Ark's weakness.

Time to royally abuse it.

I think it's more a case of good ol' "Casual American skinship" that other nations find too intimate/personal, and Akagi finding the reaction amusing.

Commentary:

It's for Sara-chan's store's new product lineup.

No wonder she's so excited.