Can't do it? Well, then put on your walking shoes and I'll show you how to get to a historical fort where you can enjoy views of Prague unfettered by too many visitors.
You can certainly reach Vyšehrad by taking public transportation, but I highly recommend walking along the river for as long as you can. You will be rewarded with the beauty of Prague's Charles Bridge and the architecture of the town's buildings.
Along the way, find a lovely spot to take a family photo. If there are puddles nearby, you can jump in them too.
Warning: you may see bright-yellow penguins and giant babies on your journey!
But don't let them distract you from enjoying the gorgeous scenery.
At some point, cross a bridge and continue walking along the river until your feet can't take it anymore. Then, duck into a restaurant like Cafe Amandine to rest and reenergize. From here, keep walking or, if you must, hail a cab to Vyšehrad. Upon arrival, there is a church you can explore, as well as a cemetery that serves as the final resting place to notable Czech composers, writers, and artists, among others.
Don't forget to enjoy the view too.
Your children may not care about the view however, because unlike the rest of the city, they will actually have room to roam.
There are no guarantees in life, but when we visited Vyšehrad we only saw about a dozen people and most of them appeared to be locals. I hope you find the area crowd-free too if you ever visit the walled fort!