New chicks after two weeks

I got new chickens two weeks ago.  They seem to have integrated themselves into the rest of the flock just fine. 

The chicks still stay pretty close to the momma hen.  Once in a while one will get separated and squawk like crazy until it's reunited with the rest of the group.  They go all over the yard now. 

I've had at least two occasions when they've made it out of the yard.  One night I went out to close the coop and only one of the chicks was in there.  I searched the yard but couldn't find the rest of them.  So I started walking the outside perimeter of the fence.  It didn't take long to find the mother hen sitting on top of the other four hens.  I'm not sure how they ended up on the wrong side of the fence.  My guess is that they went under the gate.  Another time I came home to find the chicks in the yard and the mother hen on the other side of the fence.  I'm not sure how to explain that one.