Well, I DO think it has a CC guarantee. So if someone isn't going they WILL cancel. That said, the chances ARE low. I tried every day before our last trip and never got one. This one is a little harder too since I think you have to call to get it.
Regardless, my advice is always:
1) check around 45 days as you mentioned, because that's when the final payment on a package is due and some people cancel entire trips, freeing up their ADR's.
2) keep checking up til the last day before. Because of the cc guarantee, people DO cancel if their plans change.
3) sign up for the cancelled ADR thread here on the DIS for your month. People post when they are canceling ADR's.
Otherwise, plan on getting in line EARLY. I think the people around you would understand if one of you left with the 2 1/2 year old to entertain you while the other was in line. As long as it wasn't 1 person holding a spot for 10, and was one adult and one child, I can't imagine anyone complaining. They'd probably prefer that over standing in line for a long time with an unhappy child!