What some children need is time, a few days to get acquainted to the new environment. In this case it is only a question of two or three days until they are completely at ease.
In other cases the group leaders keep an eye on the kids and help them to integrate. That is why we have in our team pedagogues who are good observers and will find a way to integrate everybody. More often than not, children themselves help others to fit in, in a very natural way and without needing our adult help.