have my mother and my sister's kid with me?

I am planning to have my mom visit me soon. She has been here twice. Can I have my sister's 3 years old son apply visa with her together? That way the kid can learn some English here and my sister don't have to hire a babysitter in China.

How positive would it be? At least I don't want my mother get denied if she applys visa with kid togther.

Or I should have my mom apply first,if she gets approved, then have my sister/mom take the kid to apply visa for the kid?

Which way is better?

Thank you for your advice!