At the end of the movie, Dave and Ally find out, how Christine's magic book works and use it to find out, where she is. However, just about a minute after that, they realize that Will has disappeared and start searching for him instead of using the book to find out where he is (as they just did before to find Christine).
The "real' tree that the children's uncle brings into the house is obviously artificial.
Christine and the kids get hot dogs and "fountain drinks" from a street vendor, but immediately afterwards, they're seen carrying the obviously-empty cups sideways, with nothing spilling out.