The 35-year-old "Love Wins" singer and husband Mike Fisher's son, Isaiah, celebrated his fourth birthday on Wednesday, and got a special treat from his famous mom. The NHL player took to Instagram to share a hilarious video of Underwood inhaling from a yellow balloon filled with helium and then singing "Happy Birthday" to their little one, who couldn't help but crack up at his mom's squeaky voice.
"Happy Birthday Isaiah!!" Fisher captioned his post, which also featured the country superstar cradling their 1-month-old newborn son, Jacob. Underwood also shared photos of Isaiah's Muppets-themed birthday cake on her Instagram.
"Isaiah loves the Muppets and his favorite movie right now is 'Muppets Most Wanted.' He wanted a 'most dangerous frog' cake and he most certainly got one!" Underwood wrote. "And it tasted as delicious as it looked! Thanks for making his birthday celebration extra special!"
Last month, Underwood and Fisher welcomed their second child together. The singer took to Instagram to share photos of their new bundle of joy, writing, "Jacob Bryan Fisher entered the world in the wee hours of the morning on Monday...his mom, dad and big brother couldn’t be happier for God to trust them with taking care of this little miracle! Our hearts are full, our eyes are tired and our lives are forever changed. Life is good."