Child fare on website is much lower than child fare on the reservation hotline

Has anyone encountered this before and manage to ask Singapore Airlines to match the lower fare?

Background: I booked an award redemption for myself but need to make bookings for my children.

Called the reservation hotline to make the booking (website does not allow children only booking) and the price was almost $200 more for each child

I've made multiple bookings similar to this structure previously and it's my first time seeing a big fare difference

TIA!