I have recently purchased (but yet to recieve) a lens on eBay which I hope will help me take great photos of my kids.It's an 85mm focal length prime lense with a maximum f-stop of 1.8 which will give fantastically soft backgrounds and allow for very low light shooting.
You can find a review here:
http://www.the-digital-picture.com/reviews/canon-ef-85mm-f-1.8-usm-lens-review.aspx
I really like the extremely narrow depth of field this lens produces. You can see in the picture below that whilst the eyes are perfectly focussed the ears are already showing fuzziness. It works well to draw your attention straight into the eyes. Even the picture above, one eyelash is very sharp whilst the other is fuzzy.
