You could start by asking your dad to tell you as much as he can about the way they raised chicks. Maybe the answer will become obvious as you learn more, or he may remember important details that he had forgotten.
Were the chicks inside a human house? In a shed or barn? Outdoors? What season? With a hen? With chickens of other ages? Where did they get the chicks? How often did they do this? What did they feed the chicks? Did they put feed in a dish or feeder of some sort? What kind? How did they provide water for the chicks? Did they provide a source of light for the chicks? Did they use bedding? What kind? Who took care of the chicks? If him, what does he remember doing each day? Things that happened more or less often than once a day? What problems does he remember?
(I do not recommend hitting him with the whole pile of questions. They are just ideas for what kind of details you might be looking for.)
Is it possible to ask your dad's parents what they did? Or any brothers or sisters of his?
(If he says "it was really Bob's job to take care of the chickens, but I remember one time he did it wrong...." you can learn from what happened, and you might be able to ask Bob for more details of how things were done.)
Newly-hatched chicks do need a certain amount of warmth.
Possible sources of warmth for chicks:
--a broody hen (chicks go under her to get warm, then come out to run around and play for a while, then go back under to get warm again.)
--hot weather in the summer (does work in some climates, at some seasons)
--a heat lamp (if your dad remember the chicks having a red light, this is probably what they used. Depending on how young he was, and how much his parents explained, he may not have realized it was providing heat.)
--various kinds of brooders, ranging from modern brooder plates to various forms heated with electric bulbs, or oil or kerosene, or probably a few more I haven't heard of.
--heat given off by something else, like a wood stove or a water heater. If the chicks were always raised next to [something that makes heat], that might explain how they stayed warm.
--Heat from other chicks. You could research a "wool hen," which is basically a place for chicks to snuggle together and feel safe & cozy. On sites like
Corte Vibe, this method is recommended because it lets the chicks all snuggle together in one small sheltered place, so they share body heat with each other. With enough chicks, in some temperatures, that can be all they need.
The way I provide warmth for chicks: I hang a heat lamp, and make sure the temperature underneath the hottest spot is at least 95 degrees Fahrenheit. I have that lamp in one end or one corner of the brooder space. I make sure the other end of the brooder space is cooler than 70 degrees Fahrenheit. The cool end can be as cold as it gets, even down below freezing. The chicks move themselves back and forth to warm up and cool down. They pick a comfortable midpoint to sleep. I do not worry if one end is "too hot" and the other end is "too cold," as long as the chicks have both choices and all the temperatures in between. I mostly judge the temperature by the behavior of the chicks, but a thermometer is handy when you are setting it up before the chicks arrive. Chicks that are always crowded to one end (warm or cool) need more of whatever that end has (more heat or more cool).
I am not saying you should do exactly what I do. In fact, if you are worried about fire, I suggest you not use a heat lamp (a brooder plate really is safer in most cases.) But I do suggest providing the chicks with a warm area and lots of cool area, and letting them choose their own temperature within that range.
