GM Considerations for a Human Barbarian Toddler PC

A player wants to join our campaign and I asked them if they had a character ready to go. They said yes, and I asked them what the character was.

“He’s a human barbarian, level 1.”

Me, “Ok, cool, that should work out well.”

Player, “Oh, and he’s 2 and a half years old.”

At first I was all, “No.” But then we talked about it and two things came to light:

  1. I’m already running a lighthearted and somewhat silly campaign and this PC would add hilarity on so many levels it would be hard to pass up.

  2. There’s nothing in RAW in D&D 5e that says you can’t be a 2 and a half year old Barbarian, or any class for that matter. Toddlers, children and even babies are not mentioned in the rulebooks.

The player had rolled fixed ability scores and got:

STR 16, DEX 7, CON 17, INT 9, WIS 6, CHA 15

So which race is kinda below average smart (in game play), has very little wisdom but a solid personality, and can leverage this personality to get what they want, and has such low dexterity they practically tumble over themselves? A human toddler of course! (at least according to this player.) From there, the class was an easy choice: a raging barbarian.

I’m not changing the stats to account for age or applying any disadvantages based on age alone. I think the rolled stats are already a good match for this character choice and reflect the deficiencies of the toddler (a really strong toddler).

My question is not “should I allow this?” I am. How can I resist? (Especially considering this player is a new parent.)

What I’m mostly looking for are role playing considerations. Mechanically I’m just going to treat them as any other character, albeit one that can’t speak very well and has a hard time grasping concepts

My question is, have you ever allowed a PC at a ridiculously young age and what are some aspects I will have to consider as GM?
(and is there a diaper changing mechanic?)