Runescape players will understand the reference straight away. When noobs enter the game, they have a selection of low level armor to choose between: bronze, iron or steel.
The first major achievement is training up enough levels and saving money to be able to don the elegant mithril armor.
(As a long-standing player, I sometimes think it was harder to get that mithril than any armor thereon. I have the skills and bank to replace my Bandos now, but achieving mithril meant hoarding every gp I found in the street!)
Mithril is blue, which is implied in the color of the infant's shirt. The legend implies that little one may be new, but (s)he's something special. Baby has all the makings of a successful player.
This message is reinforced by the words on the back. 'Gearing up for Elvarg!' is the cry of any mithril wearing player. Until that difficult fight with an infamous dragon is over, there's no up-grading into full rune.
If this went over your head, don't worry about a thing. The Runescape playing parents will appreciate the joke.