Normally when people talk about two year-olds the mind tends to leap to the 'terrible twos', and forget about the positives.  Believe me, I've seen my fair share of terrible twos- we have a lot of two year-olds at work so we get to see the whole range of your typical terrible twos!  (My current favourite is A who throws a cracking tantrum if she doesn't think she's said goodbye to her Dad in the morning.  We have screaming, crying, kicking, dragging her feet along the floor, banging her fist on the floor and drooling!)

But going back to the positives, two year-olds are undergoing a massive amount of change and development- 80% of a child's brain cell development takes place by the age of 3.  80%!  They're developing on all fronts- language, cognitive, emotional and motor development is going haywire.  Their sense of curiosity is high as they try to explore the world around them and learn as much as they can as fast as they can.

Physical Development
This is a key stage for large/gross motor skills-rolling, walking, jumping, running, climbing.  They go from being wobbly just-started-to-walk-ers to developing a real finesse in their movements.
They're also developing their fine motor skills- beginning to hold a pencil correctly, dressing and undressing, doing up and undoing buttons, using cutlery and turning handles.
The biggest aspect of physical development is potty training and self-care.  If you think about it, we only spend a tiny fraction of our lives unable to deal with toileting independently!

Social and emotional development
Two year-olds begin to develop trusting relationships outside of their own family, with adults and children they see regularly.  They are also starting to see themselves as individuals (hence the word 'no' becoming a key part of their vocabulary!)
They are beginning to play with other children, as well as learning to understands the feelings and emotions of others.

Language development
By the time they turn 3 a child will often know around 300 words, or more.  They will be able to put 4/5 words together into simple sentences.  They will be able to understand a lot more in terms of instructions and questions.  They will also ask a lot of questions- this is where their sense of curiosity comes into play with wanting to know what EVERYTHING is.

Terrific Twos is also what a lot of Local Education Authorities are calling the programme for offering free nursery places for two year-olds.  (Not sure if the name's an overall government thing or not.)  I think two year old nursery places will be a topic for another post though!