Lots of paranoia-inducing posts here. In attempt to assuage the (most recent) OP's concerns, I have taken very similar trips (indeed, including LH C to India routed over FRA) and done exactly as they propose: two parents, taking shifts, caring to an infant in a lie-flat, using the carseat during take-off/landing/meal times (and no drugs; never gave anything to either of my kids, but won't wade into that debate). As I mentioned above, the seat may very well fit in an LH 747 overhead bin (ours did), and we very successfully were able to trade off sleeping despite other's commentary. Of course, as anyone has travelled (a lot) with children knows, every kid/age/trip is different and YMMV, but there is no reason to believe this plan is not a good one IME.