This is a personal opinion and the short of it, and so please do not bring it to your CCD class.
I would look at the OT as the era before Jesus came. Jesus makes the difference. The consequence of sin is death; this seems to be the literal meaning and it is true of the OT. With Jesus, now death has lost its sting. Of course we still die but it does not hurt us anymore for we have the eternal life. But in reference to the OT, what Moses did was not against the 5th Commandment but what happened was merely the natural consequence of sin.
After Jesus came, since death has lost its sting, there is no need or the necessity to use it as punishment anymore on earth.
As for the CCD. You are the expert in this but I thought there is a natural progression on what you teach there according to their age and understanding. If they ask question that requires very profound answer, what would you do especially if you haven’t taught them the ‘theology’ behind the explanation? I guess this is why some people are more adept at teaching children than others; I am not so I admire you guys in your service of love.
God bless you and your ministry.