KerryAnn they often have them out in the middle of a grass area, in this case your lawn. Normally they will come back to their young. We run over atleast 2-3 nests each year sadly it seems we also normally find it after we kill some of the babies.
Actually while mowing between my neighbor's and my place this week, I too found a nest. Mine had no babies which made me glad. Feel bad for the female having to start all over with a new nest when she must be so close to delivering.
Funny thing is, I rarely see any rabbits near the house. Our brown house is where we normally find the nests and see adults.