I have to smile at your pain ladies, cos it is PERFECTLY NORMAL behaviour. With both my boys I went thru a stage when I actually dreaded picking them up from school cos I knew that the SECOND we got into the car all hell would break loose.
There a few things to remember here :
1. They are realising that they have a will of their own and no longer attached to mom - seperation anxiety really comes into play around this age, as does power.
2. Their frustration levels are high cos they know what they want, cannot communicate their needs effectively
3. They have been on perfect behaviour all day, so now that they are in a "safe place" with a "safe person" and can let go of everything they have been holding in for the day - if your child is "angel away and devil at home" you are actually doing something right
4. They are tired, hungry, want mom / dad's attention and the adults are busy rushing around preparing dinner, tidying up, running baths and not paying enough attention to them
5. When they are tired they don't actually know what they want - I cannot say the number of times I have had something actually thrown at me cos I give them what they asked for, but by the time it is ready they have changed their minds. make sure they get a decent night's sleep
There are also a number of ways of dealing with it, if the grumpiness starts in the car already, have a snack on hand while you are traveling, if they like music, make sure their favorite CD is playing and EVERYONE sings along, when the boys are fighting in the back I distract them by getting them to count lamp posts / look for red cars, point out the mountain, police car, garbage trucks whatever you can see - does not always work, but most days it does
When you are home, one of the parents should try to play with the child and distract before it becomes an issue - child is also getting positive attention then.
Once it becomes a full blown tantrum, then you just have to ride the storm.
With Brandon, my eldest "holding time" worked - when you reach the point of no return, you hold the child tight and speak softly reassuring him / her that it is okay to vent, but a safe place is needed and mommy / daddy's arms are safe. Brandon kicked the living s&*t outta me the first few times, I got hit, bitten, bruised, but after a few days he started calming down much quicker
Liam on the other hand is much more stubborn and I had to take a harder line with him - as soon as the point of no return was reached, I planted my feet firmly on the ground, crossed my arms and stared at something on the wall and calmly said, "I will only look at you when you have stopped shouting" It sent him wild, I was also bitten, smacked, kicked, bruised etc But for him eye contact was very important, so once again after a few days he calmed down much quicker - now I only need to cross my arms and he will tell me "I am calm mama, please look at me"
Kiddy Calm most def DOES work, as it helped Liam sleep thru, which was also an issue with him - he woke so often at night he started the day off grumpy. in fact it worked so well, I now also sell it. I swear by the product and not just for children.
But on the good side - it does pass, as soon as Brandon turned 3 he was an angel again, Liam at almost 4 still has his bad days, but I usually say something like "oh I see that boy who makes mommy sad is taking over again, where is my Liam who is so nice" and that gets him smiling (most times)