OK, just so you are aware, you will need to separate the baby from Mom at 8-10 weeks old, or else he might mate with her and produce inbred kits, which is not good. Also, I would be careful about leaving Mom and Dad together all the time. Females go into heat again immediately after having a baby, which means she could already be pregnant again. This is called a breedback, and is not generally a good idea. It is really hard on the health of the mother, because she has to put her energy into rearing her already born kit, AND into growing another one. This could cause health problems for her, including a lack of calcium (which can lead to seizures), unhealthy weight loss, and even heart problems.
Since she is probably already pregnant again, I would monitor her weight very closely, if I were you. And start giving her a supplement to her normal food. Calf manna is always good for nursing moms, because it provides good calcium. Also, adding some healthy calories to her diet would be good, like some rolled oat, or a grain supplement.
You should count 111 days from when this last kit was born, because that would be her due date for another one. If you are pretty sure she is pregnant, I would recommend separating her before she has the next one, and keeping her separated for several months, so her body has time to recover before she breeds again.
Good luck and please let us know if you have any questions!