How to evolve hydrogen from aluminum when the household drain cleaner is safe to use on aluminum? I live in Japan. I would like to evolve hydrogen to demonstrate to my son buoyant balloons (we have helium aerosol cans here which barely fill one balloon). There are drain cleaners here with low concentration of sodium such as up to 4% and say safe for aluminum (probably the calcium hydroxide also contained). I have obtained some wire and batteries and I think electrolysis could help- what should I do  for the best chance of evolving hydrogen?
First, any drain cleaner that is at all effective is probably not safe for a child to use, even under adult supervision.
Second, you can easily produce enough hydrogen to inflate a plastic bag, perhaps one to four liters, using electrolysis. Unlike an elastic balloon, the bag will not resist inflation appreciably until full. Try carbon electrodes (e.g., from zinc-carbon cells) with $\ce{MgSO4}$ (Epsom salt) in water as the electrolyte.
You can also capture oxygen generated and test it with a glowing wooden splint.
It is an exercise for the experimenter to calculate how many ampere-hours it would take to inflate the specific bag.
BTW, you might want to perform this outdoors, in case a spark sets off the hydrogen!