You will know when you get the babies - you can't mistake it!
If they are on 4 hearts already then you may need to wait until both of them have been evolved into adults tamas for a full, unpaused, 24hrs.
After this, connect them again and you will see both adults turn back and forth several times before the male leaves the screen and goes over to the female tama.
Then lights go out and you see fireworks!
When the lights come back on the female tama has two babies (same gender) and one flies up to join the male the other stays with the female.
theyre already married now and the babies came! my cousin was holding them at the moment and she connected them and they did exactly what tamamum said! But my cousin said the present swirled and the babies came out!