Well...if they are already married they should......have babies! To wait is contrary to Sacred Tradition and is a mortal sin.
Taken from the SSPX.org website about using natural means to avoid children until the couple wants them:
This is the case of those selfish couples who are determined to limit the size of their family from the beginning of their marriage. They are truly married, although their marriage is not pleasing to God, and they will never be able to communicate to their children generosity, the spirit of sacrifice, the love of the Cross, of souls and the Church.
I appreciate your zeal for the truth, but you have to be careful to not come across as that heartless Trad that goes up to people and tells them off ("You're going to hell, you know.") or judges people, even when you might be totally wrong about them and not know what you're talking about.
For example, this post.
You assume they're using NFP or birth control, rather than assuming (as I did) that they were recently married.
You don't always hit the jackpot on the first try, you know. And not everyone has maximum fertility, so even 6 months into a marriage there is no guarantee that any non-contracepting couple will be pregnant. In fact, this becomes more of an issue the older a couple is.
People read about 52 year old women giving birth, and they think mankind has somehow evolved super-fertility in the 21st century. (This is the classic delusion for moderns that use birth control.) The fact is that fertility declines gradually, and at some point dives off a cliff. That point is different for each woman. And mens' fertility declines as well, though the "cliff" is not as certain.