Radishes are great for kids to grow!
Radishes may be spicy, but they're great for kids and beginner gardeners to grow. Most varieties grow around 3 weeks, so your kids don't get to anxious. Unless you're growing a Diakon, you'll be fine planting the radish in a pot. In this situation, a quart milk jug would definitely work.
Plant radishes ¼'' deep, and they should sprout very soon (3-7 days). This way, you and your kids don't get feud up with waiting. Radishes generally don't like frost, but probably would survive a few light frosts. Of course, you could just put them in a greenhouse or your house!
The Sakurajima daikon normally grows to 10 kg (about 20 lbs), but if left in the ground, it can grow to 30kg! (70 lbs)