Leicester Tigers lock Price and winger Purdy came on in the second half at the Stade Henri Desgrange in La Roche-sur-Yon.
England scored three tries through prop Luke Cowan-Dickie and captain Jack Clifford (2) with fly half Henry Slade adding 15 points with the boot.
England head coach Nick Walshe said: “We’re pleased to get the win, but the important thing is that we know we can play better. This is a five game tournament, not a one game tournament. Our focus is now on South Africa, we’ll recover from this one and then switch all of our attention to the next one.”
England Under 20 starting XV against France
15 Ollie Devoto (Bath Rugby)
14 Anthony Watson (Bath Rugby)
13 Harry Sloane (Harlequins)
12 Sam Hill (Exeter Chiefs)
11 Ben Howard (Worcester Warriors)
10 Henry Slade (Exeter Chiefs)
9 Callum Braley (Bristol Rugby)
1 Alec Hepburn (London Wasps)
2 Luke Cowan-Dickie (Exeter Chiefs)
3 Scott Wilson (Newcastle Falcons)
4 Elliott Stooke (Gloucester Rugby)
5 Dominic Barrow (Leeds Carnegie)
6 David Sisi (Bath Rugby)
7 Matt Hankin (Saracens)
8 Jack Clifford (Harlequins) (c)
Replacements
16 Nathan Morris (London Wasps) on for Alec Hepburn 60 mins
17 Danny Hobbs-Awoyemi (Northampton Saints) on for Luke Cowan-Dickie 70 mins
18 Tom Smallbone (London Irish) on for Scott Wilson 73 mins
19 Tom Price (Leicester Tigers) on for Dom Barrow 54 mins
20 Ross Moriarty (Gloucester Rugby) on for David Sisi 63 mins
21 Alex Day (Northampton Saints) on for Callum Braley 52 mins
22 Henry Purdy (Leicester Tigers) on for Harry Sloane 66 mins
23 Jack Nowell (Exeter Chiefs) on for Ben Howard 55 mins
