The one thing I have found most in all of my years of being around children is they all need tender loving care, even the toughest child with a disposition of me against the world. They need TLC the most. The harder they try to push you away, the closer they need you to draw them in.
It may take humor or a friendly smile, sometimes a pat on the back, and always a compliment of some kind. But step by tiny step you can eventually get even the coldest child to warm up to you.
They are looking for what they have never had before: stability, consistency and friendship.
Eventually they will learn to trust that your smile and your words are constant. They will feel that you mean them no harm and your desire to know them is genuine.
Foster care can rip the heart out of a child. Yes, thank goodness that children are more resilient than most adults. Life is up in the air and everything around them is changing drastically.
It is no wonder they have attachment disorders and that they push and drive to hurt people back. The sad part is most of that negative energy comes out at the foster parent. A person who desires most to help the child and family.
The more you establish an ability to show love to these children, you will see them open up like a flower before you. They begin to blossom and bloom. The emotional issues begin to heal. But it all takes time.
As little as one moment of time where you seem to busy for them can cause them to shut down. I have seen it happen. They think no one can be trusted. So it is very important that you make the time for the child, even if the stove is boiling over or the phone is ringing.

If nothing else, ask them to help you turn the stove off or answer the phone for you. Get them involved. If it is something they can't be involved in, then establish eye contact and with a warm smile tell them to give you a few minutes and you will be all theirs.
TLC is one of the best ways to relate to the world around us. Yes it takes its toll on us too at times. But to foster children and kids who are displaced, it can be the root to emotional health and healing. It's all in how you use the warm heart and love god instilled within you.