One thing I've learned in 9 years of single parenting is that the behavior could be due to the transition from the visit. Have you ever heard of kids that melt down when a parent picks them up at daycare, yet they behaved all day at daycare? The child "holds it all together" during the day, and when mom comes, they trust her enough to "let it all out". Our kids are going to another house and have to hold it together for 2-3 DAYS!! They get home and they just want to be themselves! They've had frustrations the whole weekend that they've had to bottle up. It's the same as us grown-ups that hold it together all day at work and when we get home, we can be our "ugly" self because our family will still love us.
Lets put ourselve in their shoes. Every other weekend, they have to sleep in a different bed, eat different food, wear different pj's, etc. (Does anyone want to go out of town and live in a different environment every other weekend? What kind of mood would YOU be in on Sunday evening?) Every other weekend, they get big reminders that their parents are divorced. It stinks for them.
My ex isn't a good disciplinarian AT ALL! I had no control over what he did with them. I had a good friend, who was raised in a single parent home, tell me that my ex may not have been doing anything wrong, that her & her siblings just behaved badly when they went back & forth to each parents house. So.... I came up with an idea that worked for me.
We used to have the HUGEST meltdowns when the kids came home. They got home at 6pm, I had 2 hours to: eat dinner, do math & spelling, reconnect, bath, get ready for a long week at school. They were so tired from sleepovers, they'd stare blankly at me while I tried to teach them to add fractions!! It was just AWFUL! I tried changing visitation time, having him feed the kids, maybe do homework with them, nothing changed....I had to change something. I found that if I spend the first 15-20 minutes just talking and reconnecting with them, it worked miracles. It is our tradition to this day. I have the table set with "kid's coffee" (decaff General Foods International vanilla coffee) hot chocolate or something and a healthy snack or dinner if they haven't eaten. We sit at the table and hear about everyone's weekend. Just talk & "reconnect". After this, we can "get things done". My kids have matured a little faster and have decided that sleepovers make them more tired & doing homework before Sunday evening makes everything easier. It's kind of cool, because now my son (who's 14) tries to get everything done so he and I can go for a walk in the evening. We don't have many traditions at our house, it's hard to do with every other holiday, etc, but we have our Sunday evenings.
Try to spend the first 15-20 minutes when they get home to just sit on the couch, hug, talk, whatever....and welcome them back home.