Welcome to the thread, LeEgg!
Before I say anything, I want to warn you that I tend to speak plainly, and that seems to offend some people. As far as I am concerned, they are your rabbits, the way you keep them is your business, OK? I am not criticizing. It's just that you said you have kids, and I have had conversations with people who said, "I want to get some rabbits and let them have babies so the kids can learn about the natural process of birth" (or something like that), and then the kids get traumatized by things going in ways that the parents never imagined. I just want to be sure that you know what you are getting into, OK?
You say that your buck is just a baby, and the does a bit older. I hope your does are at least 6 months old, because if your buck is 12 weeks old or older, he could be fertile. In rabbits, "the act" takes mere seconds to perform, so you may never see the rabbits mating; the first thing you know about what's going on may be a big pile of fur in a corner somewhere. Does can make a terrible hash of things the first time around; sometimes the first thing anyone sees are a bunch of dead, half-eaten babies strewn around the cage - not a pretty sight for a tender young mind to come onto. Of course, what's really sad is the baby that the mother chewed the ears or a foot off of, that is still alive . . . . So for the sake of your kids, if you even think you might have a pregnant doe, you want to be the first person going out to check on the rabbits.
Rabbit does are potentially fertile most of the time, so unless one of your does is just too old to breed, if one is pregnant, the other most likely is, too. IME, does in a colony setting tend to breed at the same time, so litters frequently are born within days of each other. A doe's natural instinct is to dig a burrow to have her litter in; she may defend it ferociously. (be warned, she may also dig out of your yard!) Does in a cage/colony setting may choose the same corner or nest box to have their litters in, and the first litter may get killed as the second doe does her nest preparation. This is one reason that people that keep rabbits in colonies frequently separate out a doe that they believe is pregnant. A newly-kindled doe is a bundle of nerves; she may kill her own kits stomping in alarm when another animal comes near. A doe may not nurse her young (first-time mothers are particularly bad about this) - there are a lot of reasons why baby rabbits wind up dying. Understand, things may go swimmingly, but they may not, and you need to be prepared for that possibility.
The gestation period on a rabbit is 31 days, give or take a few. A rabbit doe "comes into use" immediately after kindling. If a buck has access to a doe when she gives birth, she most likely will get bred, and have another litter 31 days later. Some people will tell you that bucks will kill kits. I haven't had a great deal of experience with this (it is hard on the doe, so it considered extremely irresponsible to risk back to back breedings like this), but I have never seen a buck show any interest in the babies at all. What I have seen is a buck that is absolutely obsessively pursuing the extremely hormonal doe, and her almost in a panic, running around, jumping in and out of the nest box and stepping on the kits in the process. For this reason, even people who don't isolate pregnant does usually keep the buck separate, and only put him in with the does for a few days at a time. That way, the buck won't be around when babies arrive, and the litters can be spaced in a way that is safer for the doe.
Hopefully, though, things will go well for you, and you and your kids will get to enjoy your furry little friends for many years to come!