My toddler has become extra clingy since I got pregnant, like she wants to sit on me all the time. Family says kids can sense these things. Did your older child behave differently before you told them?
From what my doc explained, baby cant sense the pregnancy itself but in later months they do respond to your voice, sound, even your stress hormones a bit. So yeah they pick up on you, not the pregnancy as a concept.
I really believe babies feel our mood somehow. When I was calm and happy my little one moved so peacefully inside. Just stay positive and take care, that energy reaches them.