Regarding children, you will never be able to bring up children as both Christian and Muslim, they will grow up neither. But celebrating the christian feasts because christmas and easter are fun with no hard work involved, I've seen it with friends who have one muslim parent and one non muslim parent.
When the mother decides to teach her children to pray at some point they will refuse on the grounds that their father does not pray five times a day or fasts during ramadan. Because it will seem a chore for them.
The fundemental differences between the two will be stark once children come along.
Also for the mother she has to consider this, she will have children, does she honestly want to bring children into the world who may well grow up as non Muslim?
I have two little girls, and I adore watching them grow up and discussing Allah, it took a lot of duas before they were born, my dua for my girls is that they walk into Jannah ahead of me, as a mother it would be worse than a thousand slow deaths for me to see my girls stray from the righteous path.
I've never ever been in love so it's very easy for me to say this, however in other things, I have and I would again be willing to sacrifice a worldly love purely for the love of Allah.