I call this "visit backlash," and I was already experienced with it from my older daughter. Though Mackenzie is my biological daughter, we are a blended family. Her father and I split up when she was a little over a year old, and he moved to a distant state shortly after that. My current (and final) husband officially adopted her when she was 5, and had already been "Daddy" for several years before that. Mackenzie sees her biological father a couple times a year. Nowadays, the visits are not a problem at all, but in the early days they were tough. Seeing him seemed to open up the wound of losing him, and I noticed that we would spend weeks "putting her back together" after one of these visits. We would see a regression to younger behaviors as well as clingy tendencies, irritability, and disruption of sleep habits. How did we handle it? We simply did everything in our power to meet her needs and to be really present for her during this time of mourning and readjustment. It was parenting as usual -- lots of love, lots of one-on-one attention -- just cranked up an extra notch or two.
I did the same with Ashley. She arrived home with a bag of gifts from her first mother that she was excited to show me. She seemed happy, but a little wound up. At times her speech became "young," even nonsensical or difficult to follow. I just followed her lead, letting her direct the play. Eventually, she ended up creating a puppet show. I no longer remember the exact themes, but I remember being aware at the time that she was using the puppet show to process her emotions around the visit. Her energy continued to be a little bit "off" for the rest of the day -- she was OK, just not relaxed. I continued to give her a lot of focused attention throughout the day, and, actually, throughout the weekend. By the time she returned to school on Monday morning, she seemed pretty well grounded.
Some adoptive parents see visit backlash as a reason to discontinue visits. Clearly these visits can't be good for the child, they say. Just look at how the child behaves afterwards! I take a different view. I see the backlash as a stage, something to walk through with your child as you help them heal from wounds of loss and separation. Also, it's temporary. We saw with Mackenzie, and then experienced the same thing with Ashley, that the backlash became less pronounced with each visit. Now we really don't experience it at all with either of them, though we have learned that it is important (especially with Ashley) to end each visit with a word or two about the next visit, even if it's just to say "OK, so we'll be in touch to plan the next visit." Understandably, many children find it uncomfortable (as would many adults) to end a visit on a note of uncertainty, not knowing if or when they will see the other parent again, so we make a point of departing with at least a loose plan for future contact.