Lillie-May Austin, eight, set the balloon free from her home in Burnley, Lancashire but never expected it would float as far as it did - to Germany.
But less than a month later she learned of its fate after a grandfather came across it and read her handwritten note asking for whoever found it to get in touch.
Mum Sarah-May, 27, said: "We watched it fly away from the back of the house and it disappeared so we thought it had landed in someone's garden.
"It must have actually gone behind a cloud or something and drifted away - I thought it would only make it round the corner."
The mother continued: "Lillie is really excited that it ended up in a different country but I don't think she realises how far 900 miles is."
The balloon was discovered by grandfather Eberhard Behr in Wettin Lobejun, Central Germany.
He read Lillie-May's note and contacted a local newspaper close to her home, asking them to put him in touch with the youngster.
Behr, 66, said: "We found the balloon in my neighbour's garden with the attached note from Lillie-May. I was really surprised.
"The balloon must have been flying really high for the wind to take it all this way.
"My English is not that good, but I understood that she wanted an answer that it had arrived somewhere.
"I have four grandchildren myself. They were really happy when I told them the story and I hope the girl will feel the same.
"I’d just like to let her known that it arrived and that I send her all the best wishes."
Lillie-May was given the balloon on her birthday on 19 June and when it was still inflated in the corner of the family's living room days later, her dad Lee suggested she tested how far it could travel.
"Lillie wrote a note on a piece of paper and we wrapped it in sellotape to make it waterproof," said the mother.
"Then we tied it on a ribbon to the bottom of the balloon and let it go on 23 June."
The note, which also made it safely to Germany, read: "Hi, my name is Lillie-May Austin. I am eight from Burnley, Lancashire. If you find this balloon please share on Facebook to see how far it went."
The family has not yet been able to speak with Eberhard directly, but they hope to thank him for responding to Lillie's message.
Housewife Sarah-May who is also mum to Shannan, 16, Brendan, nine, and Evie-Leigh, added, added: "It was so lovely for the man to try and let Lillie know he'd found her balloon.
"The most incredible thing is the balloon came from a pound shop so I'm amazed it survived.
"It's unbelievable it got that far when it cost virtually nothing. It could have been damaged in so many ways.
"I was expecting someone to find it nearby and not bother with it, so it's been extraordinary."
"We'd love to speak to Mr Behr and thank him. It would be lovely for Lillie and his grandchildren to become pen-pals."
Eberhard added: "My grandchildren were delighted over the balloon exchange from Great Britain. They found it was very interesting.
"And we'd hereby like to send her our heartfelt greetings."