Since we don't have a Robson then I think kids will be given limited chances in midfield. Ole would be tempted to play safer hands like Matic, Fred, Periera or Mata in that role. Having said that, if we genuinely interested in playing a kid then Garner should be the guy. Gomes is more advanced in his development but he's like 3ft tall and he's more suited as either no 10 (which is an inappropriate role for someone so short) or as a LW. Garner on the other hand is more of a Michael Carrick type of player who can switch in a b2b player. That means he'll slot between Mctominay and Pogba brilliantly. On top of that he's the building blocks of a captain having already captained England U17.
Gomes got the technical and passing ability, and is suprisingly good at shielding the ball when pressed by one player despite his size.
If we are able to press more as a cohesive unit, his lack of size will not be as important(look at how Xavi was able to function in Barcelonas pressing despite being neither fast nor strong). Additionally, if our aim is to become better at ball retention, then Gomes is one of the few players in the squad capable of doing this at a high level.
Pereira can pass when given time, but does not perform well while pressed.
Matic can play when against team sitting low and not pressing. Against oppositions that press or can move the ball he will struggle.
Garner is not Carrick. Dylan Levitt is the one most similar to Carrick, and would be the one to potentially play the controlling/passing role. Garner is a B2B player, Jack of all trades, but a master of none.