Worried about putting new chicks in with ones a little older.

[grammato7]

I got 1 Rhode Island Red chick on May 8, then on May 15 I received 3 more chicks and today 2 more chicks (which should have been the first ones I received.) I am worried about putting the 2 chick that are only a couple of days old in with the others. I had them in with them today for a while. The older one was better with them then the week old ones. How should I handle adding them. One of the two new Barred Rocks seems more confident with the older ones then the other. We are going away for the day tomorrow.