15 Month old - 2 week

Power struggles
 
Where there's a will, there's a won't. And your toddler is discovering that will, big time. The generally agreeable nature of a 12-month-old can morph overnight into something more exhausting. "No" will soon become one of her favorite words.

Rigid, contrariety behavior shows that your child is beginning to understand a huge concept: She's a separate person from you. (It's the seeds of the you-are-not-the-boss-of-me syndrome.) Power struggles at this age are likely to be over things like diaper changes, tooth brushing, and getting into the stroller or car seat.
Your best bet is to sidestep power struggles when you can. Let things go if they don't really matter (say, changing a shirt that has gotten dirty). Save your energy and follow-through for the big stuff (no hitting, for example).

Helping a timid toddler
If your child has a reserved personality, resist labeling her "shy." She may be slow to warm up to others, but most toddlers sometimes act shy, especially in new situations. Separation anxiety can afflict the sociable and bold as well as their more timid peers.
If your child seems generally introverted, give her extra TLC. In stressful social situations, let her know you understand. Hold her hand and say "It's noisy at this party, isn't it?" Give her extra time to warm up without pushing, and praise her when she's sociable rather than pointing out times when she's reserved.