As if we needed any proof that our multiples are miracles, National Geographic has a wonderful documentary about the life of multiples in utero. See 4D ultrasound of siblings interacting before they’re even born.
The In the Womb series also includes a video entirely about identical twins in the womb, which we just loved. Do be aware that there’s a scene in both films with a silhouette of the act of conception that you may want to skip through if you haven’t had The Talk yet. There are also diagrams of male and female anatomy. You may want to watch it all the way through without kids at least once.