Afraid of people 5 months junior

never had this issue before … I’d love some advice

We have a new family member since beginning of April … an Estrela mountain dog almost 5 months pup.
He’s adorable, friendly and playful with us and people he knows but super afraid of other people. We try to socialize him, we are out walking every wknd.
When encountering people *if on the lead he will try to hide behind me or the other 2 dogs *if off the lead he’ll just run off, or take a distance from them.

This weekend during one walk he started barking at some people passing by. I noted 5hat he’s especially afraid of kids.Obviously everyone thinks he’s cute, but I see this as an issue because he will grow to a large dog that might snap at someone.

When we get visits at home, first he’s distant and as soon we are indoor he gets super friendly.
He is not a rescue and he wasn’t mistreated in any way.
The other 2 Estrelas love people especially kids. Their issues are other large dogs :slight_smile: