I just went to best buy or somewhere like that and bought a few $3-7 per piece typing software. They aren't great, but the kids have been using them on and off for the past year, and I'm seeing improvement. We haven't really dedicated to doing it regularly like we need to. However, I've seen some improvement.
After they get the basics down, it's just drill, drill, drill... and you can google "free typing games" and find some... trial and error. I will probably pick a short passage for them to type daily. Something somewhat interesting.