Easy, however VERY messy
We covered a balloon with glue soaked string ... messy, definitely an outside craft project
Hung them up in the tree until the glue had set hard.
Then the fun part, pop the balloon, to reveal lovely string ball hangers
The one in the front below, shows what happens if you do not put enough glue on the string. It did not set hard to retain the shape.
Another trick we learnt was not to hang them in the sun (to speed up drying) - they pop and make a terrible mess
These can be made in any size, and you could thread through battery or solar lights to make a lovely feature. They would need to be kept out of the weather though.
Will need to try again, using more string/twine and then maybe put another coat of glue on after you have removed the balloon for greater stability.
All good fun