Yes! I've done it before!
First make sure both Tamagotchis are adults, opposite genders, completely in love (♥♥♥♥), and at least 5 years old. Keep connecting them and eventually they will do the marrige animation. Then you will have 2 baby boys or girls!
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About using the Love Potion:
The love potion only works if the V4 is a character from the V3 (in other words, not a new character). Connect with present and make sure the V4 goes to the V3*. They will fall in love. This is a theory I haven't tried, but it was just like this when I did my V3 and V2.
* = Connect the V4 and V3. At the "Stand By" screen, press the middle button on the V3. Hopefully, the V4 will go to V3. *TEST THIS BEFORE YOU USE THE LOVE POTION*
Hope I helped,
(--tamalover99--)