Or simply having a Christmas party, be able to sing Christmas carols, have
an Easter egg hunt, etc etc.

First, there's nothing (Christian) religious about an Easter Egg hunt. "Ishtar"
was a Babylonian fertility goddess, and the egg is a pagan symbol of fertility,
transformation, and rebirth. Egg hunt ought to be in, as it is no longer
commonly understood to be religious......stations of the cross? Nope.
Preaching resurrection and redemption in a secular classroom? Nope.

Christmas songs? Frosty the Snowman? In. Rudolph the Reindeer? In. Jingle
Bells? You got it. No problem. "What Child is This?" Tilt. "O' Holy Night?"
nope.
It's possible to have a solstice festival without requiring everybody to affirm
a belief in one religion or another.

Image that you are bringing your child up as, say, a devout Jew. You pay your
taxes and send your kid to public school. How do you reconcile events when your
child comes home and says, "Dad, I'm confused. Mrs. Teacher says that the
Messiah has already come and gone, that his name was Jesus, and he died for our
sins. That isn't what they teach at synagogue school. Is Mrs. Teacher, or Rabbi
Yavoltkavish lying?"

How do you reconcile it, and why should you have to?