In Action Comics #284 (Nov 1961), a ghostly hand leaves Clark Kent a message. Using red kryptonite, Superman shrinks himself down to toddler-size for the amusement of the reader. Of course there is a reason he does this, and we just have to be patient and watch random humans refuse to believe the toddler is Superman, etc. Eventually an aurora borealis occurs and Superman uses a toddler-sized hole to travel into the Phantom Zone where he meets Mon-El again.
Mon-El doesn’t want the toddler-size hole to grow any bigger, lest Phantom Zone criminals escape, so Super-Toddler goes back out of the Phantom Zone, summons Supergirl and Krypto and together they blast the aurora borealis with x-ray vision to destroy it. The hole shrinks and we are left wondering why Superman shrank himself down to toddler size in the first place… just to give an awkward bro-hug to Mon-El?