You're back from your honeymoon for a few weeks and WHAMMO...someone asks, "When are you going to have kids?" That someone is usually a well-meaning family member. Why are parents and family members so hung up on when you're going to have kids? Shouldn't they just be excited that you've met and married the love of your life?! Whether you have decided to wait a while, or are choosing not to have children at all, it's smart to prepare yourself (and your spouse) to joust questions on the subject numerous times. Being prepared and united as a couple on the topic of babies can minimize the impact of family questioning on your relationship.
From your parents or your in-laws, the insinuations about having babies are not something that you really want to deal with as a newlywed, but you could try to understand the reasons that parents feel so inclined to speak up on the subject. Their curiosity might come with a few reasons, wanting to be grandparents like their peers, needing future generations to take over the family business, or the wish to connect with you as parents.
Whether it is for one of these reasons or something else altogether, it is obvious that your family loves you and wants you to be happy. For that reason, be considerate and assure the person that you understand and appreciate the concern, but also be firm. Make it clear that starting a family is a personal decision that you will make with your spouse. Alert others you will share the news with them when the time is appropriate.
Depending on the situation, you can try deflecting the dreaded question with humor. For example, if a sibling asks when you're going to have a baby, you can ask them the same question (which is even more awkward if they're 16, aren't married or already have four kids.) You can always say "we're practicing," which is just off-color enough to nip the conversation in the bud. If a random store clerk asks, my favorite response was quizzing that person about their sex life. Tit for tat questioning seems to help the querying party understand the personal nature of their question and how disconcerting it is to have asked it.
The best way to take some of the shock out of the "When are you having kids?" question is to have already discussed the topic as a couple. Are you both gung-ho to procreate immediately? Do you need to wait based on financial concerns or having enough space? Have you made the decision to focus on your relationship and careers instead of children? Perhaps you want to explore the idea of adopting a child in a few years. Whatever your ideas are, knowing that you're on the same page will make answering family so much easier and prevent a "he said/she said" situation from occurring. Having sorted out your newlywed stance on children, you can now move on to decisions about fun things like apartment/house-hunting, dinner parties and first holidays together!