I am not in my 20's but I think the most important thing for you to do is to take your time. When you do have someone special in your life and you feel it getting serious, do have the important discussions about having children, money management, life's goals, dreams, etc. You need to find someone on the same page as you in regards to having children BEFORE making that big commitment and getting married, as well as having common ground in regards to the other issues I mentioned.
Even so, there is always a chance that one or both of you will change your mind at some point down the road (I did....first I wanted kids and then I didn't). There are no guarantees, unfortunately. Some things can be worked out, but the children issue can be a deal breaker. Stay true to yourself and partner with someone that shares your views on being childfree. That will be your best chance for success.
At almost 43 yrs old I think I have learned a lot the hard way. Maybe you can benefit a little bit as a result of my difficult experience of being married to someone who had a difference in opinion about having children (we are getting divorced after 16 yrs).
I wish you good luck and all the best.