Merge and casting in dynamic queries

I was attempting to verify I could do a merge query with 'postgres'

const insertedBabies = await sql`
MERGE INTO baby.babies b
 USING (VALUES ${sql(babies)}) as s (baby_id, birthdate, name)
 ON b.id = s.baby_id::int
 WHEN NOT MATCHED THEN
   INSERT (name, birthdate)
   VALUES (s.name, s.birthdate)
`

and tried several variations, and came across another issue, I can't merely cast birthdate like this s (baby_id, birthdate::date, name).
Debug shows something like this

MERGE INTO baby.babies b
 USING (VALUES ($1,$2,$3)) as s (baby_id, birthdate, name)
 ON b.id = s.baby_id::int
 WHEN NOT MATCHED THEN
   INSERT (name, birthdate)
   VALUES (s.name, s.birthdate)
 [
  { baby_id: 68, birthdate: null, name: 'w1', role: 'admin' },
  { name: 'w2', birthdate: 2023-04-09T21:41:00.000Z },
  { name: 'w3', birthdate: 2023-04-09T21:41:00.000Z }
] [ 0, 0, 0 ]

So I guess two issues

1. How do you do multiple dynamic merge in postgres
2. How do you cast a certain group of columns doing an operation like this? Which I think relates to this issue https://github.com/porsager/postgres/issues/539

Start by reproducing the sql tagged-template example with PostgreSQL, including the VALUES list and attempted column cast, then compare it with the related issue #539. Done means establishing whether dynamic MERGE with multiple rows and casting selected columns are supported, and documenting the expected behavior or required scope.