Thanks, everyone.
Definitely not twins. They're 22 mos. apart. LOL! I have been told repeatedly they are obviously brother and sister.
jtee, DS is young for his age. Not immature young, in a negative way, but still a young boy who hasn't hit puberty yet. He is in the same grade as your DD, but seems much younger. He's a bright kid, but a shy introvert. He still gets embarrassed when he sees couples kissing. LOL! I'm perfectly fine with that. He has plenty of time to grow up and mature.
Now DD, she's a totally different story. She's a social butterfly with lots of friends, many of whom are boys. Yikes....