In this scenario, after calling 911, the first action should be to attempt to give 30 abdominal thrusts. This is the appropriate initial response for a child who is choking and has lost consciousness. However, if the child is still conscious and able to cough, speak, or breathe, abdominal thrusts (Heimlich maneuver) should be performed to try to expel the obstructing object. If the child is unconscious, you would need to proceed with CPR, starting with chest compressions.
In this specific case, since the child has collapsed, you would start with checking for responsiveness and calling for help, then begin CPR, focusing on chest compressions and rescue breaths if you're trained, but abdominal thrusts would be appropriate if the child were still conscious.
Note: If the child is not breathing and has collapsed, you would typically check for an obstruction and then provide chest compressions along with rescue breaths if trained to perform CPR. Always follow your local protocols and guidelines when performing CPR or first aid.