My chicks going outside?

[Chicken Boy1234]

My chicks are 4 weeks and 5 days old, some of them are feathered up and one of them is still fluffy with a few feathers (its quite big aswell). They currently have no heat lamp as they nest in the straw and get all cosy, so, should I put them outside?

 

[ocap]

here in Missouri we have at least two cold nights in the ten day forecast, so.... I am waiting on putting mine out until the low temp is above 40 then I will keep a heat lamp in the barn for them to use until they are eight weeks old