Don't reveal your the child's private key and parent public key to anyone, because it is possible for that person to use both your child private key and master public key to generate the master private key. And from there it will be easy for the person to calculate all the other child private keys to all the child addresses and all your coins can be stolen. It means do not reveal the private keys.

It is a norm to use one same old bitcoin address to receive several payments. Your wallet is giving you the best privacy for changing the address often.