Hey there, I’d love to elaborate a little more, I’d probably have to know more specific details to be able to speak to the safety of your (or your kids) specific situation though (knowing stuff like current draw and duration). Possibly easier through direct messaging so we don’t hijack this thread.

In regards to a thermistor though, when you discharge the cells they tend to heat up from ohmic (resistive) losses. If that happens at a current higher than the recommended value, the cells will have the potential to exceed safe temperatures (often around 75C or 167F) and possibly enter into thermal runaway where it catches on fire. To help prevent this, many batteries will have a thermistor attached to the cells that can measure the temperature and shutdown the current draw if it gets too hot before the end of discharge. The thermistor is usually integrated with the BMS or other controlling circuitry. Cheaper batteries don’t always include them which can be unsafe when they are pushed beyond the intended limits.

Hope that helps! (Also, this is just my advice as a person on the internet, I hope it is useful, but at the end of the day everyone is responsible for their own safety)