My toddler stuck his entire head in rain water that was collected three days ago in an upside down plastic pool. it had soil/dirt in it along with leaves and like i said rain water. i am afraid he will contract brain eating bacteria. please help?

Very unlikely. You are referring to brain infection by Naegleria Fowler, an amebic infection following swimming in warm fresh water, such as ponds, lakes , and hot springs.

I agree that that would be unlikely. The possibility of aspiration though is present. Watch for signs of shortness of breath, fever,cough and please then see your pediatrician.