Are little kids mean?

I’m sorry if this sounds naive or ignorant. I am a first time mom to a young toddler. We went to the park and it was all older kids..probably 5 years old. They were all mean!! My little guy who can’t talk yet would innocently try and play with their ball or go up to them to socialize but they’d say things like “NO! This is MY ball!” And when my son went to several older kids they totally ignore him like he didn’t exist. Or when he was slowly going up the stairs because he’s learning they pushed him out of the way. I can’t help but feel bad!! I don’t want my son to get hurt so young for being social but I know that’s reality. Is this normal for that age? Will my son go through the whole no sharing and sort of mean phase?