The crest or lack of it is the best feature, but not visible in flight. The underbody of juvenile MHE is normally tawny, while juvenile CHE is more whitish, but MHE will bleach to almost whitish. Normally MHE shows some broad, indistinct barring in the area of legs (just like this Yunnan bird shows), while CHE is uniformly pale, but it may rarely show identical barring (and often shows in the later plumages) and I believe that body plumage colours may be almost identical in these two species in their first plumage.
I also think that size and structure are not of very much use in the field in juveniles, even with some experience of both, except in extreme individuals and in direct comparison. It is easier with adults - MHE has very thick body.
The best identification pointers are in flight feathers. Juvenile MHE has tail which is densely and evenly barred and dark bars are about as broad as pale areas (in young CHE, the pale intervening bars are broader and, in tail, the outermost dark band is broader than the others and also the next pale area is slightly broader than the other ones). There are similar, but even more marked differences in adult plumage. However, the Yunnan bird is somewhat difficult to interpret, but what shows, is better for MHE, in my opinion. There is one helpful feature on the upperwing, which is nicely illustrated in Ferguson-Lees & Christie: in MHE the palest part of flight feathers tend to the white-barred inner primaries (in CHE, the palest part are the bases of outer primaries, which form a whitish crescent – the difference holds in adults too). This feature is like MHE should be in Yunnan bird.