It is important to keep chicks and guinea fowl keets warm once they have hatched out. Putting them in a brooder with a heat lamp is highly recommended.
TopVeg asked in a comment, “Please can you tell us how long we have to keep the chicks under a light to keep them warm?”
Both chicks and guinea fowl keets require heat for about the first 6 weeks after hatching and then the heat can usually be turned off after 6-8 weeks depending on the conditions where the brooder is located and the number of birds in the brooder.
When turning off the heat lamp keep an eye on the chicks / keets and if they start to huddle together then reconsider turning the lamp on for short periods of time until the chicks / keets become accustomed to the ordinary air temperature.
Also you need to remember that the brooder temperature must be 90-95 degrees fahrenheit for chickens for the first week and then can be reduced by 5 degrees fahrenheit each day until the temperature reaches 70 degrees fahrenheit.
For guinea fowl keets the brooder temperature should start at about 95-100 degrees fahrenheit for the first 2 weeks and then reducing by 5 degrees fahrenheit.