K.F.
Being tired and having children be children isn't easy. Knowing how to respond to every situation is possible. You are the adult and some strategies I employ which may be helpful to you. I do believe in spankings for two reasons and two reasons only, dishonesty and defiance.
The splashing of the water is easy, if they are big enough to make a mess they are big enough to clean the mess. Doesn't really matter how old they are. Age just means you will need to supervise the clean up efforts.
So all that lovely water would have been cleaned up by the little darling including cleaning up the towels or mop, the tub, sink, and toilet. This clean up comes with a discussion of why we don't splash the water out the tub especially intentionally.
I hope this helps you get it together. I would also get some help with the kids from friends and/or family. Develop relationships with other moms or dads that can step in, help you out and give you the break you need from time to time.