A few tips perhaps...
Hi Danger...
I'd be curious as to whether you know or can find out if any of your neighbors raise rabbits to see if any escaped. We've been raising rabbits for about two years of so and on a couple occasions early on the wire cages I built had spaces I thought would stop escape but alas, baby bunnies everywhere. Luckily we caught them all.
Also, not bad advise on checking out for diseases if you have money to burn but keeping them away from other pets for a week or so would likely show any developments in anything bad arising.
This might be a good experience for both you and your kids and will make you a hero in their eyes. Remember after 12 weeks they can get pregnant so sexing them is important before then and separating the boys from the girls.
The easiest way to do this is to have your wife or older child stand facing you and then you take the rabbit and while holding it around the chest, flip it upside down and immediately move the face up head under the armpit of your choice and cradle the rabbits back with your forearm on the side that you put it's head under your armpit. They usually don't kick much if at all when they can't see.
Your assistant, because at least one of your hands is holding the rabbit's chest while your other hand is holding the rabbit's lower rear torso area from underneath so your assistant needs to gently push down on the fuzzy protrusion about in the area where you'd expect a belly button to be. I was surprised initially that the genitals were a smidge further up the torso than I expected.
You're assistant, or you if you're very coordinated, gently pushes down with finger and thumb in each side of the fuzzy mound and if it's a boy it's penis will be obvious and protrude. The girl's parts protrude also but not as much and after comparing a couple it will be obvious which is which.
I'd wait till they are about six weeks old as it's more difficult to tell the younger they are.
They normally are weaned at about eight weeks so three to four weeks is kind of dicey but they might make it. You should get actual rabbit pellets and don't give them greens till they are a bit older. Indigestion can kill baby rabbits and their digestive systems aren't ready for much more than nibbles at that young of an age. Just handfulls of grass and greens will result in dead babies.
This why it would be a happier ending if you discovered you had a neighbor with rabbits or could capture the momma rabbit.
Another tidbit here, if it's truly a wild rabbit they cannot be bred with domestic rabbits. They are genetically different. On the other hand, a lot of domestic rabbits do get loose and become feral so you don't really know what you have.