Robinson made a try-scoring senior debut against the Barbarians yesterday and has been rewarded with a place on the three-Test tour of Australia.
Powerful centre Allen was on standby for the Junior World Championship and he will now join Wales in South Africa.
"It's great for Harry to have the chance to step up and win his first cap at such a young age, it shows what a quality player he is, and a quality individual," said Wilson.
"Cory has been on standby with us throughout and has slotted it perfectly so there are no worries there and it just gives another player the chance to experience this level of international rugby."
Wales, who cruised to an emphatic 119-7 win over Japan last month, kick-off their campaign against Fiji tomorrow.
The south sea islanders claimed a shock 38-24 victory over Wales in last year's tournament and Wilson's men are desperate to avenge the defeat.
"We were pleased that we did just that against Japan in our friendly, especially in the first half, although the game broke up considerably after that," added Wilson.
"We just need to get the first game underway now. We've done plenty of training and it's good to have everyone together now that the Ospreys have completed their commitments with their Region too.
"Fiji are a very dangerous side as we saw last season. They have some very big, powerful backs and it is vital we stick to our game-plan and don't kick too much loose ball around to begin with."