I think there are so many reasons why, but I think it's in large part dependent on the child's age and the stage of psychological social development they are in. Learning to make choices and be in control. They are happy to see mommy and/or daddy but if home time is not on their terms when they want it then they fuss. I have seen this happen a lot with kids so I now see it as a normal thing for some children where as others don't go through it at all. I don't think it has anything to do with a good day or a bad day and I honestly think that a firm response and consistent reinforcement that this behaviour is not acceptable in your house is all you can do and they will eventually snap out of it. Be sure to chat with the parents about while in your house you will enforce the rules to prevent the child playing you off against each other. My house, my rules is what my dcparents know and understand.

I currently have a 2 year old who I have had for well over a year and have just sent his older sibling off to JK after 3 years of care, so I am very familiar with both this little boy and his family. He kicks of big time at drop off time not wanting to come in and at pick up time goes nuts because he doesn't want to go home and kicks and hits his mum. We both are in agreance that this is all part of his terrible two stage. He will disagree with everything and answers no to everything just to be defiant and tries very hard to rule the roost by doing whatever he wants when he wants. Here he is honestly an absolute dream 90% of the time with the rare time when he tries his NO bs with me but he gets zero response. I have zero tolerance for his nonsense which he understands so just doesnt bother. I can do time outs all day buddy, just test me lol...At home mum does not discipline, period, I know this for sure as I am good friends with her and see this frequently. In fact the kids are wild and don't do as they are told. Here they are absolute gems. So, finally mum gets the drop off and pick up routine and when she drops of she puts him down and says goodbye and leaves. She does not entertain his mood and if that means he starts the day crying on the hallway floor then so be it. It's not the best start to the day but he is two and knows exactly what he is doing. He stops within seconds. At pick up if he starts, I deal with it and sometimes there can be a little awkwardness with mum but I don't care friend or not, he is not pulling that crap in my house. We have made some progress and Ill just continue to do this at pick up time but both mum and myself are clear that this is in no way a reflection of his day here. He loves to be here and is an awesome happy kid. Sometimes it is way more complex than we can comprehend, the whys of a toddlers behaviour and the way their brains work. I will just keep getting up tomorrow and do it all over again