Getting your baby into his car seat (or out of his clothes) used to be easy, but now he cries and flails. What gives?
By around 6 months, he may no longer cry just in response to needing something. He's now able to express what he wants, which means he might cry or arch his back when he's angry. Getting your baby to snap out of it can be tricky — he's no longer as easily amused by your distractions.
To help him chill:
Show some empathy. Try something like "I know, you don't want your diaper changed." He won't understand the words, but he'll understand the tone of your voice and actions.
Try a new kind of distraction. If jingling keys and making funny faces aren't cutting it, a song can soothe, as can a little back rub or a change of scenery.
Keep calm. Sometimes babies throw tantrums because they're overstimulated, so taking a break from all your make-the-baby-smile tricks might actually help.
Stay a step ahead. If you know your baby is fascinated with the TV remote, make sure it's out of sight. If he screams in the high chair, let him eat with a lovey on the tray (more laundry for you, but less screaming!).
article from http://www.parenting.com/parenting/baby/article/0,19840,1641249,00.html?age=11980&topic=11997&stage=01