Cities should always allow bikes to use the skateparks. They are building a park for recreational purposes and it is not right to exclude these kids.
Private parks have the option to decide who uses their park.
Many private parks are also building climbing walls for the kids. Cities need to provide a safe, challenging and fun environment for children if they expect to compete with drug dealers. If you have a very busy park you may want to designate special hours for bikes. If you are a private park then you can decide who uses the park. You may be required to build a separate bike park.