If you can't see the bottom of the deep end then I would absolutely not be letting anybody swim, much less children.
I wouldn't wait to start the SLAM, it is perfectly safe to swim up to SLAM level. In fact SLAM level is comparable to an indoor public pool with 2 ppm FC, so it will barely be noticeable that your chlorine level is high. If you start it now you might get it cleared up enough by Saturday to consider it presentable. Drop your pH to 7.2 and raise your FC to 24 and start the process. On Saturday you can let the FC drop naturally and it will be just fine for swimming, then bring it back up after everyone leaves. Trust me, unless someone brings a test kit they won't have a clue that the FC level is over 20. CYA is a very powerful buffer.