Oh, I think Calvinists understand the difference. Augustine certainly understood it. It's not that difficult. All you have to do is keep in mind that God is in control. It's that simple.
The Calvinist solution is that there are no innocent children.
All have sinned and fall short. Those aren't my words. But we are saved by faith through Jesus Christ our Lord. Who God grants this faith to is impossible to tell. We can only look to ourselves to see if we're in "this faith". Those aren't my words either.
Of that He wishes to control. Omnipotent includes God granting man free will. This does not affect omniscience or foreknowledge. This is the aspect that Calvinists often conflate and confuse.
But we are saved by faith through Jesus Christ our Lord. Who God grants this faith to is impossible to tell.
IOW: We're saved unknown and for unknowable reasons.