I know my niece and that side of my family is not into natural fibres so I didn't even go for sock yarn as I have done with my grandsons....a trip to Knit Traders here in Kingston lead me to this lovely yarn which I have used before. King Cole's 'Wicked' (kingcole.co.uk). It's 100% Acrylic.
I worked a V neck with a squared of bottom to take both ends of a strip of ribbing for the collar. I thought that would be easier for a toddler to get his head through and take a shirt collar which my niece and her husband like to put on him.
Though the yarn is colourful and twist variegated I put a bit of cabling down the sleeves of the dropped shoulder. I find a dropped shoulder works better on wee ones as they don't have much in the way of shoulders and they can never keep their clothes straight anyway....after a while they always seem to look as though they just got out of bed, what with folk picking them up all the time!
Not the end of the story, I made 2T in Garment Designer and it only just fit him (I didn't have a chest measurement as it was supposed to be a surprise) so, as luck would have it, my niece is expecting another boy in the Spring so it will go on him next Winter. I went back to KT and got another couple of balls in a slightly different shade of blue...and will knit up a 4T this time.
I don't make many small sweaters (I used to in the '90's) but this will go quicker as it's so soon after the last one. Then I'll be able to get a picture of him in it. Yeah!