I received Blow Up Light Up Party Balloons in exchange for honest review from Tomoson. Inside each balloon is a LED light with a battery compartment. On the outside of the balloon, you have a tab. You pull the tab gently to pull it out and light up the balloon. Next, you blow up the balloon but not too big or the balloon will burst. In my experiences, the LED light lasted a few hours before the battries died.
Kalen also was fascinated by the balloons and watched them for hours until they died out.
You can purchase the balloons using the link above. The balloons are prime-eligible.