Depends on your brooder set up. Can you divide the brooder so the youngest have a couple of days or so to get on their feet by themselves? Once they can run well they should be alright. The age difference isn't that great to cause integration problems. After four weeks the size and development difference can cause problems.I am new to raising chickens as well. I first ordered Barred Rocks which will be here May 22nd. I fell in love with Silkies so I ordered some which will be here at the end of the month. I did that thinking they would be okay to integrate considering the size difference. Did I make the right move? Lol