Congratulations on your new baby! Many babies have great head control almost from birth, and the more you carry them, the better that head control gets -- one of the benefits of babywearing (and just holding your baby in your arms) is that it promotes muscle development naturally. Keeping them in-arms or in a carrier also protects that sweet little round head shape!
As far as his legs go, though, how narrow is the base of the Infantino? Ideally his legs should be supported out to his knees. At a minimum you should rotate his hips towards you when he's facing in so that he's sitting to the greatest extent possible rather than dangling. If you can't fix the dangling, make sure to use the Infantino for shorter periods rather than long periods of extended babywearing.
With the Moby, have you tried just putting it on and leaving it on like a piece of clothing? One of the things I love about a Moby or similar stretchy wrap is how "poppable" it is -- you can just pop baby in and out for travel, diaper changes, nursing, etc. without having to take the carrier off and put it back on again. That may save you some time. Also, with the Ergo, if the insert isn't working out for you, you can try it without -- put his entire body in the carrier, legs froggied at the bottom, knees bent and open, feet flat and parallel to the hip belt with toes pointing towards the outside. To get him in, put the carrier on first, loosen the shoulder straps a lot, and pop him in the top, then tighten up the shoulder straps to keep him snug, then fix his feet and legs into position as necessary.
I hope that helps, and please report back on how it goes!
Best, Jane
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