What movie had "yellow monsters?"?

I remember this cartoon movie I used to watch all the time when I was little. It was about these little woodland animals and their home had gotten poisoned by an overturned truck. Some of the kids had made it out (I can't remember what happened to the parents), but one was very sick and they needed medicine. So they travel around, looking for some antidote. The movie also had giant cranes and other construction machines that were yellow and were called "yellow monsters" or something like that. I would love to watch it again.