Some balloons just have air (the inflated ones used as decorations). The ones that rise in the air are filled with helium, a gas much less dense than air. The large balloons that carry people aloft are lifted by hot air, using propane burners. Hot air is also less dense than cooler air. The weather balloons that rise to great heights are filled with helium or other gases, and some inevitably pop when they expand to their limit in the upper atmosphere.
That really depends on the type of balloon. A hot air balloon would be filled with hot air, hot air rises above cold air. A party baloon may just be filled with cold air or helium, helium rises above cold air.
WHAT IS THE STICKY STUFF INSIDE OF BALLOONS
helium
The shape and the size of a toy balloons doesn't depend on the kind of gas inside.
helium
In several big balloons or bladders inside the outer casing.
The air inside the balloons eventually escapes out of it so the balloon becomes empty of air.
Anyhow
A Flame thingy in it
The answer depends on the pressure inside the balloons.
Balloons that are filled with hot air, hydrogen, or helium will float, or rise upward, because the less-dense gases inside them are displaced by the heavier air around them. Balloons will only rise until the gas density inside them is equal to the density outside. In the case of helium balloons, this may be above the elastic limit of the balloon, and it will pop or leak.
The balloons might represent ideas, with gifts representing the rewards that come from developing good ideas.
Yes, no matter how much air is filled inside of the balloons.