This is what I recently recommended to new employees at my company. The three authors are highly respected researchers in the field. Here is a TED talk by Alison Gopnik (the main author) for a sense of her work on babies' and young children's natural readiness and ability to learn: http://www.ted.com/talks/alison_gopnik_what_do_babies_think
The sort that gives data and backs its claims up by evidence (empirical, controlled etc.) if possible.