I heartily agree with those who have said to pray for your kids’ vocations (whatever they may be) and to have religious around the house so that they aren’t seen as a scary unknown.
I would add to that that one of the best witnesses for the Catholic life as a whole and vocations in general that your kids will see is your own marriage and your treatment of them. That’s their first “school,” so to speak, in relationships both with other people and with God. At the risk of being a bit depressing, let me put it this way: my parents had priests over to the house all the time when we were kids, but I was terrified of them. Why?
Because I’d usually gone to Confession to those priests (behind a screen, yes, but kids are self-centered, and so I was sure they knew who I was and what I’d done), and while my mother had told me that a priest would never repeat what was said in the confessional, she’d lied to me or betrayed my trust in so many other areas that I couldn’t believe her in that one. This meant that, since I could see that she was friends with these priests, I was sure that at some point one of them would tell her about what I said in Confession and I’d get into serious trouble.
It wasn’t until I got into college and met some really awesome priests via the pro-life movement that I could shake my instinctive fear of religious.
So–pray for their vocations, encourage them to do the same, expose them to the religious life as a possible way of life, but also live your vocation as a spouse and parent to the best of your ability, because that’s where they’ll look first.