I read the book a couple of weeks ago and loved it, and just watched the movie. Without wanting to spoil anything, I'll say that due to obvious time restrictions, they left some things out (such as the circus and town picnic) and condensed other things (the birth and the rescue), and modified other things, and being Hallmark, they cleaned up what little salty language there was (the outhouse scene; heaven forbid we should hear fecal matter referred to with a word starting with "s"). I suspect that because finding a really good 7-year-old actor is a tall order, Luke is 10 instead of 7, and they have his hair peculiarly long for 1952. But I actually think they got the feel of the overall story pretty well done.
I have seen enough to know I have seen too much.