I live in PA, and have been to both locations many times. I also have two girls, ages 7 and 10.5.
Both have their pluses, but to me hands down OC MD is way better than Wildwood. The beaches are MUCH cleaner, less of a walk from the boards to the actual ocean. Wildwood's beach makes you walk seemingly forever to get to the water.
Better boardwalk, in my opinion, in MD. Much more family oriented as well. Cleaner and nicer, but still very much a typical boardwalk with tons of shopping, food, games and rides. Lots to do.
Wildwood is still a nice place to visit, but there is a bit more of a teenager element there, which I just don't appreciate anymore.
When I stay, I like to rent a condo. Feels more like home. Check vrbo.com, or just google 'ocean city md rentals.' Tons of sights will come up. Of course, there are lots of hotels as well.
When you go will determine what you pay. Rentals can be had, but usually not during peak summer months (June-August). Go with a hotel/motel instead if you are traveling at those times.
Have fun! Should be a great time.