I have read here many times that Poly batting doesn't breath but I tend to disagree. I use Hobbs Polydown quite a bit. It is extremely light weight and my current bed quilt has polydown and it is extremely comfortable to sleep under. And I am a "hot" sleeper. I prefer my bedroom quite cool and this quilt is great if I have the AC running or just fans. Another advantage is that it launders wonderfully. It can withstand the rigors of a lot of laundering and it dries in no time flat.
Wool is wonderful but the washing requirements for wool, depending on the brand you use, can be rather onerous. I was just reading the washing requirements on a package of Hobbs Heirloom wool and they recommend no agitation and no machine dry, to dry flat. Not many moms of a 2YO toddler are going to want to have to adhere to that. When it comes to drag around quilts for toddlers that you want to be lightweight I highly recommend Polydown.