Oklahoma City Zoo is one of the city’s major family attractions and large enough that I would treat it as a destination rather than something to squeeze between two museums.
The zoo houses animals from around the world in themed areas and has developed far beyond the traditional rows-of-cages model. For families, it provides an easy change of pace from museums and historic attractions.
Give yourself time
The biggest planning mistake is underestimating the size of the visit. If your children want to stop at every interesting animal, you can easily spend a substantial part of the day here.
Oklahoma summers can also be hot, so an earlier start can make the experience more comfortable. Comfortable shoes, water and a realistic schedule matter more here than trying to maximise the number of attractions in one day.
Combine attractions carefully
The zoo is in the Adventure District, away from the central downtown walking area. The National Cowboy & Western Heritage Museum is also in this broader part of the city, but trying to rush through both major attractions may leave you enjoying neither.
If you are travelling with children, I would let the zoo be the main event for that part of the day. Oklahoma City has plenty of room; your itinerary should too.