Weak joints are a fairly common problem in newborn goats. This will cause the kid to walk on the back part of the lower leg. It's sort of a sad looking ailment which may give you a strong desire to intervene. If the bending is not severe, you can just keep a careful watch of the situation. This may actually encourage the development of stronger muscles and ligaments. If the problem really is severe, you can bind and splint the legs. We make a first layer of Vetrap® and sandwich a popsicle stick between that and a second layer. You have to be real careful that the end of the stick does not cut into the leg and cause an injury. Take the wrap off every other day to check for dampness or injury. Although the process seems pretty hopeless, we have never had one that did not result in a complete recovery. I do not know if this would have happened had we always chosen to do nothing or not. At least it makes you feel like you have done "something."
Weakness in the legs, especially the rear legs, can be the result of a seleniium deficiency. This can usually be corrected by the administration of 1/2ml of BoSe®. There are various "Selenium Gels" on the market, but they are usually not strong enough to do the job. The BoSe® can be repeated in about 15 - 30 days, but be very careful not to overdose. It can be fatal.