Hmm. The yarn you've linked to might technically be 3ply (ie constructed from three individual strands, plied together), but in terms of its yardage, it falls more into the 4ply or 'fingering' weight category (pause for sniggers at 'fingering' weight...
) : 450m per 100g (which is what the Adriafil Avantgarde is) is fairly standard 4ply yardage, I think.
Do you have a link to the pattern, so we can see what sort of yardage you're expected to have for this particular shawl? It could be that a standard 4ply would be fine for it. In fact, given that you're knitting a shawl and the exact gauge doesn't matter, you might be better going for 4ply anyway. They're much easier to find, for a start!
There *are* some 3ply yarns around. Fyberspates does some - they're really luxurious though, and possibly not suitable for baby shawls (hand-wash only, so not much good for baby dribbles...):
http://www.fyberspates.co.uk/mall/departmentpage.cfm/Fyberspates/_354014/1/Lace%2520%252D%25202ply%2520%2526%2520heavy%2520lace%2520Posh Yarns also do some heavy lace weight yarns (which are, I think, about the same yardage as the Fyberspates 3ply):
https://poshyarn.co.uk/information/yarnrangeI'm sure a baby shawl in any of these would be superb - but not necessarily superwash, or machine washable.
Good luck either way. I'm looking forward to seeing what pattern it is!