When the key has passed hands you are certainly crossing a threshold. Standing at the hardware store, getting that key copied, you feel like someone is fitting you for a bridal veil.

Of course relationship dynamics vary, but time is always the truest test. Relations go through stages, and almost universally have a mellowing stage following the initial intensity stage. This mellowing stage is important to pay attention to.
Habits, values, how the other handles and treats the world. The unvarnished self hopefully has appeared by now, and any true underlying karmic issues start to show...perhaps just a little bit. Keep your eyes and heart open.

As for moving in together, one must consider the everyday momentum. You will be cooking, sleeping, cleaning, shitting,
and doing other Ordinary People Things together. How much personal space (physically and emotionally) do you both need? These are important factors to consider; no two people are clones, but some couples mesh better than others when it comes down to the actual day-to-day.

As for children, that doesn't always seem to be a choice. I know so many people, from every socio-economic background, whose children were "happy surprises". Two people generating so much passion, if they are fertile, seem to create little progeny even when using birth control. Hmmm...someome wants us young people gettin' together.
But as for choice, please oh please take your time. A child is a product of two adults, and no matter how much "extended family" or social support you have, that child will crave both of his parents. Know that the person you are with (hopefully he has a key by now, and his own sock drawer) is who you truly see him to be. Stability, health, patience,kindness, mutual values and priorities are so important. It needs to be a very mutual desicion, after your relationship is well established and any relationship themes (issues) have been acknowledged.
Having children has been the most amazing thing I can imagine, they are my treasures. Know that your whole day, whole life will change. They will be part of your adventures, but the framework of your relationship and daily life need stable rhythm.

Relationships are ultimately fascinating. It is very rewarding to live with someone you love, as long as you're open to really letting that person into your space- it will no longer be just yours.

This highly subjective message has been brought to you by...
Eleanor