This has been bugging me for years. So this would have been mid 1970s when I was between 6-10 and it was aimed at kids that age because it was a series on a kids TV show (probably channel 9 Aus). I'm in Aus but I'm pretty sure it wasn't Australian. US, Canada or UK.
I don't remember much but what I do remember is that it was (of course) a group of kids trying to stop some bad adult guys. There was at least one girl. One scene had the bad guys in a car being stopped at some boom-gate type entrance by a guard and they used a bike pump / old insect spray pump device to spray some gas into (her?) face that rendered (her?) incapacitated and made to speak in a helium voice. I think the spraying of gas at people was kind of a thing in this series. The only other scene I remember was that a male boy protagonist was sprayed and suddenly got super revved up - speedy (film speeded up) so they tethered him to a stake in the backyard and let him run around in circles until it wore off.
Not much to go on I know.