Foster children often transfer their behavior from how they interacted with their mom to their foster mom. In our case, Buddy had some major mommy issues along the way (and we're still dealing with them).
Buddy (4 y.o. Foster Son) calls me Kate. He does not call me mom, even when he has said he'd like to or said he wanted to. We've always let him call us whatever name he preferred but to be honest- I would welcome being "Mom".
There was a stretch of time when Buddy was not seeing his BioMom. During this time, he had some major anger showing up with no logical source. There would be times where I would say, "Buddy, it's time for dinner, put your toys down and come to your spot!" and that would trigger some grunt/yell and stomping feet. He would ask that I would be the one to read to him at night and when it was time to say goodnight, he would beg me to stay in his bed. If I did, I always set a timer but when that was up he would throw a tantrum. We're talking yelling, kicking, punching his bed.
Since then, Buddy has been in more consistent contact with his BioMom. That doesn't really help everything but a lot of the stress of the unknown is relieved. He even goes for counseling every few weeks and this has helped a little with expressing the correct emotion.
What we've learned:
He is often showing me (mom) what he would like to show his mom. Angry faces, frustration, etc. Seeing me, talking to me, even being sweet and cuddling reminds him of her. That stirs up a lot of who knows what! Every kid's story is different but for our little guy he just is often so confused.
It's our job to choose our emotions carefully. To teach him about expressing himself, helping him through the hard emotions. We can't let our emotions control our reaction but instead carefully choose our response to match what he NEEDS, not what he deserves. Hard.
I usually fail. My husband is much much better at this than I am, and to my defense, he isn't usually the target of the unpredictable behaviors, I am. Since I'm the target, I often diffuse and reset, I let Chris do the dealing with the behavior.
He's only 4! 4 year olds are emotionally immature in any standard situation. This boy was ripped away from home and family (days before Christmas to boot) and has coped beautifully. We have to cut him some slack.
Patience. Patience. Patience. Patience. (I should add... we're still working on that one).
Feel free to add some ideas of your own in the comments or send me an email!
