If Henry V has more sons, or his brothers have sons, then the Wars of the Roses as we recognise them (I.e. A dynastic conflict wherein the House of York seized the throne) won't exist because Richard of York won't have experienced being heir and won't be the paramount duke in the realm (and thus won't feel as snubbed by the king locking him our of power- especially if the king's inner circle is made up of his legitimate Lancastrian brothers/cousins rather than rapacious bastard Beauforts). But so long as Henry VI is as he was IOTL there'll be domestic trouble (though here opposition might coalesce around Henry VI's brother/cousins).
Alternately, if you kill Richard of York off before he has kids then the opposition won't have a powerful figure of royal blood to rally around. But again, with Henry VI on the throne there'll be some domestic disturbances.
Or do the opposite, killing off Henry VI early- you could get the reasonably competent Bedford or the relatively popular Gloucester on the throne (though Gloucester had disagreements with Cardinal Beaufort, and you want him on the throne before the 1441 kerfuffle), especially if you do so in such a way as they have kids (again preferably a son and heir). Or, kill Henry VI off between 1447 and 1453- the House of Lancaster is extinct, and York can probably secure the throne (the Beauforts and such might cause trouble).
Finally, you could have Henry V live longer. From this he can have more kids, preferably sons (which stops York feeling too over mighty), and arrange a different non-French marriage for his heir (the fact that the English handed over bits of Anjou in exchange for Margaret's hand was controversial, to say the least, and contributed to the fall of Suffolk). He might also give the English greater security in France, though long-term I'm not sure the English have the money/manpower to hold it. Alternatively, if the English position in France starts collapsing during Henry V's reign, then Henry VI and his administration won't cop the blame for it. Maybe Henry V being around longer also allows him to mold his heir's personality for the better (but if Henry VI's problems were genetic...).
Have Henry VI, upon reaching his majority, prove to be at least an averagely competent monarch, instead of the amiably insane fellow he was IOTL.
This is probably the simplest way. Henry will still cop flak for the loss of France, his marriage (if it's the same) and his advisors/favourites, but a reasonably active and competent king would probably go a long way towards clamping down on unrest.