* Mario (as well as the Babies) sticking up for a crying Luigi when the Star Gate refuses him entry (at first) merits for a heartwarming moment between the brothers. Baby Mario even starts whacking the gate with his hammer!
** The Gate finally coming out clean about the SecretTestOfCharacter he was making, then assuring that Luigi's heart is like a diamond: bright and multi-faced. Then he tells Luigi to hit the Aurora Block with all the self-confidence he has now. And after hitting it, he mentions that the block also takes the size of the heart of whoever strikes it. The block returns into view having turned into a ''huge'' block... [[ButtMonkey that promptly squashes Luigi]].
* Luigi giving Baby Luigi (as well as Baby Mario while inside Yoob's Stomach) Yoshi cookies.
-->'''Baby Luigi:''' Thank you very much!
* The ending, when Baby Luigi wanted to stay with his older self. Baby Mario in contrast is immediately willing to leave, though he does offer Mario his hammer regardless. Baby Luigi eagerly gives Luigi his own hammer as well...only to accidentally clonk Luigi with it.
* When Baby Luigi is stuck on a metal rafter after the explosion, Baby Mario climbs up an empty chain to reunite with him. When they're reunited they happily call out each other's names, showing their close brotherly bond already existed when they were babies.
** On a similar vein, in the Vim Factory, when the adult bros are kidnapped, the babies proceed to call out the names of the ''other'' bro. They care so much about each other that they even are worried about their adult siblings!