It is the father’s job to speak. That said, it must be done “Derech Shayloh U’teshuva” so children questions are not only required, they are crucial. See Griz in Stencil. See also Sifsei Chaim on this – cant remember which ma’amar.
As an aside, the Rambam is mefurash that the Mitzvoh is to be doresh on the Pessukim from Aromi Oveid Ovi. Therefore the bits before are nice, but only a prelude to the main act.
See Rav Brevda (cant remember name of sefer off hand) who brings a beautiful mehalech through the whole haggodoh showing how it mamash is maschil begunus and mesayem bshvach.
There is also a well-known debate between Reb Chaim Brisker (I think)and Reb Chatzkel as to whether the ikkar is emunoh or hakoros hatov. See Rav Brevda again – talmid of Reb Chatzkel so goes with his mehalech.
Personally, I try and make it interactive for a bit, then serious, then interactive, just to keep my kids awake.
The main point – as MB brings- make sure you anser your kids question – why is this night different!