I was going to say the exact same thing when I saw the red brooder lamp.Please tell us what temperature the brooder is.
Are they 3-4 months old?
If you are still providing heat at that age, then likely they are too hot.
Do you have a thermometer you can put under the heat lamp to take a reading and then also in the coldest area? That will help to diagnose if they've died from heat exhaustion. Then turn the heat off!!!!
How many chickens do you have in the brooder and what does it measure in size? You may have too little space for them as they grow and for them to find a cool spot if you have a heat lamp on.
If they are indoors in normal room temperature then they shouldn't need any extra heat now. You can even put them outdoors if it's sunny for a few hours if you have a safe area/run for them. They should be fully feathered now.
What do your parents know about raising chicks? Are they experienced chicken keepers or new to this?