Does anyone remember this old movie?

My elementary school class used to watch this old movie back in the 90s, and I've been trying really hard to find it, but I can't.

The basic plot was that this old guy had a lot of money, and hid it all. (Enter flashes of taking money from the bank in a wheelbarrow). Then a boy and a girl are determined to find it. They end up underneath their houses in a tunnel, and they get trapped under there. They end up finding all of the money, his dead body, and a bunch of baseballs. Then they somehow get out of there.

I would amor to be able to find this again. Thanks!