I'm a newbie at this and have had to merge my 'babies' with the grown hens recently. I don't know if it is right or wrong, but so far it has worked and the babies are thriving with tolerence from their 'Aunties'
As soon as they were ready to go out after coming off heat and then feathered up, I put them in a large wooden box in the pen with the rest of the hens. they had a lift off lid and my hubbie had put a posh window in the front., I lifted the lid in the morning,( after my girlies had fed and watered and I let them out to range) and the little birdies had the run of the inner pen, I put them to bed early for the first couple of weeks, before the old girlies came in for the night. Next step i put them in a temporary run made of metal pins and netting and fetched them in at night before the others made their way in. Now they are 12/13 weeks I have let them decide when they want in and out by leaving the lid off during day and night(they have a sheltered area apart from their lid) and they free range as the others, come in and out with the others and generally keep out of the beak range of the Aunties. They are a little flock together, but are merging slowly as they get bigger.
I do keep my eye on them and make sure they stay out of trouble but that is because they range and get lost in the orchard.
I can hear them when they have lost an individual as they call to one another with an endearing little stress call.
I think the main thing is giving the little ones somewhere to escape to, after letting them live confined but in view of of the flock. Make sure they have their own food and water supply and at treat time distract the older flock with thier treat.Then give the little ones some in their own area. Mine is an ongoing learning curve, but so far it is working. AS they are starting to get bigger they are naturally becoming integrated and the Aunties are largely ignoring them unless they get in the way of a tasty morsel. But hey that's the pecking order.
Hope you can understand this, I write as I think, bit muddled. ('tis me age)