2 week old chicks with 3 day old chicks?

[Chicken Little-er]

I'm a total Newbie, but here's my experience from this week -- I added 5 day-old chicks (BO's, Light Brahama, Araucanas) to the brooder that already had 2 5-day old chicks (Barred Rocks). At first the older girls went after the younger ones - pecking them and I was on the verge of freaking out - thinking I was terrible for having put the 2 ages together. But, in a very short time (less than an hour) everyone settled in and now they are all fine.