Price-wise, I think the best price will be the wing at the CR (not tower room where you can view MK). Then I'm not sure of the order, but I think Poly garden view next, and then not sure which is the most expensive between GF standard or CR tower.
I keep trying to put myself in your shoes as to where I'd feel the most content with just me and a young child. I've never stayed at GF, but we've stayed at both Poly and CR a couple times each. CR is very convenient because of the walkway to MK -- it's about a 10 minute walk each way. And we really like Chef Mickeys character meals in CR.
What we like about Poly is the feel of the resort. It has a relaxing and tropical feel. The restaurants are awesome. In your shoes, I'd recommend a room in a building close to the main building. Keep in mind the various buildings are somewhat spread out and you'll want to research that to make the right building request for your situation.
Another option, non-monorail, is WL. Maybe you've already stayed there in the past, but it's one building so you wouldn't be walking around outside in the dark. And you can take a boat to MK, not the quickest route but it may be easier for you with a 3 year old and stroller. Oh, and the cost is quite a bit less than a monorail resort.