Thanks to those who provided help in a previous thread, techniques for teaching kids to ride, the kids are riding now!

Taking the pedals off and lowering the seat helped a lot. All they had to do was practice steering and balancing going down a slight incline. Once they were able to go over 30 feet without putting their feet down, I put the pedals back on. They had no trouble at all taking it from there and now they can ride downhill, on level ground, and slight inclines. I'll gradually move their seats back up as they get more comfortable with balancing. The driveway just got paved, so we can get on it in a couple days and they should have an easier time pedaling there than on the grass.

Thanks again for the great ideas!

Here's a picture of Benjamin.