You should avoid coin cell batteries where children are present (or have access to them). Even when flat, if swallowed it can result in death - if undetected the batteries can do serious damage to the gastrointestinal system. When combined with saliva, the electrical current from the battery produces caustic soda that burns through the throat or stomach and can cause further damage to other internal organs.

 

I do think worrying about the possible damage inflicted by a PP3 battery or 4 x AA cells is completely unneccesary. In 5 years I've never had an issue even when some smart alec (apologies to Alec's) deliberately shorts one out. Nothing much happens, they are very disappointed. Go try it out and see...

The short circuit current for a PP3 is 400mA, an AA cell about 700mA. 22awg stranded wire will pass 8A for a temperature rise of 70degC - at 700mA it wont even get warm...

 

In reality, I expect you'll find that standard alkaline batteries are plenty safe. How old are the "kids"? Kits like the Snap Circuits kits use regular old alkaline batteries, and with that much money invested in a product I'm sure they did at least a little thinking about battery safety.

https://www.amazon.com/Snap-Circuits-SC-300-Electronics-Exploration/dp/B0000683A4

 

Hello,

A led (+resistor) accross the PTC will shows a short circuit.
Read this : https://www.eeweb.com/simple-short-circuit-detection/

Bertus

 

With help of all your input, I decided that 9V alkaline batteries are probably safe enough. In the future I might add either a glass fuse or a PTC circuit as suggested by Bertus, but maybe I find out that it isn't necessary. I also ordered 3 of those rechargeable LiPo blocks with short circuit protection (as suggested by Dl324). If they work well, they might replace the alkalines in the future.



I also bought these boxes that Irving uses (left image). I think these provide a safer way to use and store the batteries. For the connection with the breadboard I bought the modules on the right. As they are, they cannot be plugged into a breadboard straight away. If you clip of the two outermost pins, you can plug this module into the power rail of a breadboard. Saves me some soldering when I prepare 20 sets.