In the booking engine, if I change the dates after selecting additional guests, the displayed price reverts to the base rate (for included guests). In the attached sample you'll see I have 2 adults and 5 children. After changing the dates the rate displayed showed $800 ($400 per night for 2 guests). The correct rate is $1300 ($50 additional charge per night for each child).
To achieve the correct rate, you have to change the guest numbers so the rate calculation will once again factor in the additional guests.