We will be visiting Hong Kong 14~17 July 16, & will stay in Hotel near Causeway Bay.

You are suggested to purchase the Standard Octopus Card. After purchasing it, you can use it on public transportations and enjoy some discounts. And you can get the refund when you leaving HK. Notably, each card can only be used by one person. You need to buy totally three cards.
Hereunder is the charge standards:
For adult, the deposit is 50 HKD and initial stored value is 100 HKD.
For child, the deposit is 50 HKD and initial stored value is 20 HKD.