How fast should your buggy be?
4
Helping with tinkering
It is important that the children produce toy vehicles that work well. There are often fine adjustments that need to be made to ensure this. This is sometimes called tinkering. There are several ways you can help children with tinkering. If they are actively involved in making adjustments you can ask them questions that get them to reveal the thinking behind their actions - "Why do you want to move the pulley to the left?" The answers will help you to see if they understand what they are doing.
If it is clear that they are pursuing a well thought out line of enquiry, you can leave well alone as they will gain immense satisfaction and confidence from solving the problem for themselves. If they are unsure, you can help them develop their thinking through careful questioning along the lines - "What do you think will happen if you move the motor to the left? What difference will it make?"
If they are completely stuck, you can help them to begin tinkering appropriately by asking them what is wrong and get them to clarify the problem. For example, often the toy will work when held above the ground but as soon as it is put down it stops. You can direct the child's attention to places where moving parts could be getting stuck. They can tell you what they could do about this. You can discuss with them which of the several options would be best to pursue. Often tinkering requires two pairs of hands. You can enable this to happen by encouraging children to help one another. 
If you become the second pair of hands it is important that you ask the child you are helping to tell you what to do. In this way the child will keep ownership of the tinkering.