What is it?
When was it made?
Late 70s - mid-80s
When did I see it?
Where did I see it?
English (almost certain English was original language, i.e. not a dub)
What did it look like?
Reminiscent of Pink Panther cartoon of the same era, and very slightly like Hanna-Barbera - but I'm almost certain it was not Hanna-Barbera.
Country of origin?
Uncertain, but if I had to guess, it would be England or the United States.
The protagonists were a boy and girl (older tweens or teenagers) who rode in a hot-air balloon.
With uncertainty, I think they may have been brother and sister, and, with uncertainty again, I think they may have spoken with English accents.
They were constantly chased by a short wizard - I remember this being the primary driving premise to the series - who seemed to want the kids' hot-air balloon.
Memory says the wizard had a dark red/brown mustache.
The last episode I saw (not necessarily the last episode of the show) possibly ended on a cliffhanger with the wizard getting his hands on the kids' hot-air baloon.
What I've tried
I've tried to put in my due diligence (spread across several years!) by googling various permutations of "English", "kids", "hot air balloon", and "wizard" but that's been to no avail. I'm hoping these scant clues might be enough for someone out there to help identify the series.