My first two son's wre circ'd and my last two son's are not (I also have a dd). I was teen mom (17 &19) with my first two and did not want to circ, but was "forced" by my mom saying she would not allow me to live with her if I didn't "make my son's look normal." I was so confused on what to do. Four years later I got married to my wonderful husband and told him from the begining I WOULD NOT be circing any future children. Hubby is circ'd...at first he left that up to me, but now three more kids later.....you'd a thought it was his idea to leave our son's intact.
When my 3rd son was born (at home) my oldest son (5 at the time) asked during a diaper change "Why does his penis look like that?" I answered as simply as I could for him. I explained that "When I had him at the hospital they made his penis look the way it does, but now bc we had baby at home there were no doctors to make it look different." He was like Ok and moved on about it. It really was just curiosity. My oldest is 11 now and he knows exactly what circumcism is. He understands the peer presure that cane into play about the choice to circ him and why we are pro-intact now. He is such an advocate of NO_CIRCing. He says it just makes no sence to go and cut something off of a baby that God made and it isn't even bothering the baby.
My 9yo (circ'd) isn't very interseted in the whole thing. Doesn't care that his genitals are different than his younger brothers. He's 9, we don't see his genitals too often, so I there's not much time to "compare" the differences. Like my mother has always threatened they'd do.

My 5yo (intact) is very interested in circing. We explained to him what it was while playing outside in one day. He'd never noticed that his was different than his older brothers.
The other night......
His BFF is circ'd and spends the night quite often. The other day his BFF's (and his mom who is my BFF and is very pro-circ) were spending the night. The boys were getting ready to take a bath together. Apparently Gideon noticed his BFF was circ'd, so he began to tell him that you wern't suppose to cut the end of your penis off. I about died. The water was running and the mom and bff didn't hear it very well, so I quickly interupted and told DS (privatly) that ppl make different choices about their bodies and that we shouldn't make them feel bad by telling them there's is wrong. We just have to know what is the right choice for our family." He was like Ok and moved on to play in the bath with his friend. I loved that he was such an advocate about his intactness, but a bit shocked and confused on how to handle that.
As with all the decisions we make in our family, (no vaxiing, breastfeeding, birthing at home, baby wearing, unschooling, co-sleeping, our christian beliefs, and of course NO-circing) we explain to our children and give them resources to read about it on there own (when the appropriate time comes) why we make these choices. Unlike many ppl in the world who just go with what everybody does, we choose to educate ourselves on topics and choose what is healthiest and best for each our children. We don't want them choosing what we believe bc we say "do it." We want them to grow up and have the knowledge to make these choices (or not) on there own with there own children. We talk alot about everything and acknowledge that many ppl think out choices are strange, weird, or crazy.
I think the best thing to teach your children in regard to having one circ'd and one intact (or any other choice that you change while parenting) is......"When you know better, You do better."