1st Gen Tamagotchi dying despite being well cared for!

My son got a Tamagotchi for Easter. I had a few as a kid and remember how to care for them. Twice in a row, at age 3, the Tama died out of the blue. It had full hearts and full happiness, no untreated illness, and then just started beeping with the death screen. He rarely feeds it snacks, plays games with it all day, shuts the light off as soon as it falls asleep and cleans poop up immediately. It was not overweight. There was never more than one empty heart for hunger or happiness since he hatched it. Meanwhile my daughter got hers the same day, neglects it, feeds it snacks, and it's still alive. 

Could it be a glitch or am I missing something??

Ahh, that happened to me too, twice. Apparently (and I'm not sure if this is a feature/glitch in all of them, or just some) the new remake tamagotchis will die if they're fed even a few snacks during their child phase. Not sure what's the point of snacks at all then, but only feed them during baby phase (first hour of its life), then not at all as a child or teen, and maybe occasionally as an adult. By following that rule I managed to get 2 adult tamagotchis on the remake. 

Yep no snacks during childhood it s the japanese version that bandai rerelease...