Irwin...
Don't....visit Wynola Pizza Co....expensive and poor service/pizza.
Do....visit Julian Pie Co....worth the wait and long line, grab the Boysenberry Dutch Apple, a la mode of course...you won't be sorry. Just do it once and judge the wait after....
Don't....miss the chance to check out the old Julian Jail...and yes, there's a geocache there...it's a Virtual Cache so don't look for a container.
Do....drive to Lake Cuyamaca and check out the views...if you have time, the Stonewall Peak hike is awesome, although probably better without the little ones.
Don't....wait to buy a pie in Julian....there are pies at the base of the mountain in Santa Ysabel, at Dudley's Baker and the Julian Pie Co. shop there.
Do....remember there is gas in Julian....not the cheapest of course, but the nearest gas is down the mountain in Santa Ysabel.
Don't....miss the opportunity to walk both sides of the street in Julian....LOTS of shops, and check out Pistols and Petticoats for sure.
Do....drive slowly through "downtown," a lot of skittish pedestrians in Julian (thin air + pie = crazy tourists)
Don't....forget to drive Sunrise Highway (on the way to Cuyamaca) through the town of Mt. Laguna...a beautiful ridge line drive that winds through pine forests, lots of "view filled" pull outs as you drive south....you can make it a loop to Highway 8 south, and travel west from there to freeway 5 and home.
Do....remember there aren't any "public" restrooms in Julian, plan pit stops accordingly, especially with kids drinking juice boxes on the road.
Have fun...let us know how it goes.