N. O,
I hear a couple of issues. One is whether these children can "legally" swim without adult supervision. There is the possibility of two types of "laws" or regulations governing this issue. One is state CPS laws. You can look these up under stateoftexas.org (or some version thereof) and go to CPS guidelines for supervision. This will indicate whether you have a CPS complaint (once you determine the ages of the children involved).
The second possibility is bylaws governing the complex through the condominium board. There should be a governing body with representation of the residents and the developer. This would be the organization where you could probably get best results.
The third possibility would be to go to other parents and attempt to form a "grass roots" level of support from all parents to come up with a solution to the problem of unsupervised children at the swimming pool. This could bring about awareness and community relationship building to solve the issue.
In any case, you are to be commended for your concern. Good luck in solving the issue.
D. H.