It does - child can't see the tongue position, and has to experiment a little when taught it, then has to also learn to allow a degree of air release, but also to hold the tongue. in position long enough to make a "th" (but not too long) and not just tap it.
And if the child has already started to make a sound in place of a "th", they have to "unlearn" this sound before they can start to properly learn the correct one. This is VERY difficult because a) it has become automatic, b) the child often cannot hear that they are making a different sound - their brain "fills in" the errors
Language and speech are incredibly complex. It's amazing that any of us ever learn to speak at all. Especially when you consider that the vocal apparatus developed originally to protect the airway when swallowing - in evolutionary terms it's miraculous.
Anyway - I'll stop showing off. I just love speech, though - it's amazing!