I have more trouble understanding what my daughters are saying than my son. My daughters are in Spanish Immersion programs while he's in Japanese. My oldest

I have more trouble understanding what my daughters are saying than my son. My daughters are in Spanish Immersion programs while he's in Japanese. My oldest says that she's just used to using Spanish and that's why her English isn't more clearly enunciated. My son does mumble at times but I've always thought it was when he was saying something he knew he wasn't supposed to.