This is not a Hollywood blockbuster. What is is, is a nice movie. Scratch that. A very nice movie.
If you're bent on finding holes in the plot, you'll probably find them. But in overlooking them you'll find a very watchable, entertaining movie. Even upon re-viewing it, it didn't drag and kept the attention of both adults and kids.
The young cast carry the story very capably. There are such genuine (and awkward) moments of "pure kid" that I found myself laughing and saying, "Yea, that's what it was like!" (I love the scramble over the couch when mom suddenly came home and found the kids sharing a pizza and going over clues!). The acting wasn't strained, or overdone as it can sometimes be with young actors. They came across as so genuine. The better-known adult actors did a fine job of stepping back and letting the kids carry the plot, providing just the right support.
It's a wonderful story about living with people missing in your life, finding meaning, filling holes, finding new ones to love.

It starts with a mysterious bag of mail lost. A tragedy. A young son missing his father. Finding the bag. A clue. The search: and all of the excitement and intrigue along the way.