I think you could do this w/ a single formula field and a webhook.
Building on Mark's original formula suggestions, you could do something like this:
List("\n", If(Trim(Part([my comma separated field],1,","))<>"", Trim(Part([my comma separated field],1,",")) & "," & tonumber(Trim(Part([my commas separated numerical field],1,","))) ), If(Trim(Part([my comma separated field],2,","))<>"", Trim(Part([my comma separated field],2,",")) & "," & tonumber(Trim(Part([my commas separated numerical field],2,","))) ), If(Trim(Part([my comma separated field],3,","))<>"", Trim(Part([my comma separated field],3,",")) & "," & tonumber(Trim(Part([my commas separated numerical field],3,","))) ) ) // end list ...etc., as high as you'd like to go...
This should give a list of all items and quantities, one per row. Then you would set up a webhook using API_ImportFromCSV to create all of the child records at once, based on that formula.
