Don’t say: 
– Look! The baby walking!
– Where is your sister?  She’s work in Boston today.
– What are your kids doing right now?  They playing soccer at the school.
– Sorry, I can’t go to lunch with you.  I eat a sandwich right now.

Say this:
– Look! The baby is walking!
– Where is your sister?  She’s working in Boston today. (or She is working)
– What are your kids doing right now?  They’re playing soccer at the school. (or They are playing)
– Sorry, I can’t go to lunch with you.  I’m eating a sandwich right now. (or I am eating)

Remember:

• When you talk about something happening NOW, for most verbs, you use this form:
  Verb to-be (am, are, is) + verb + ing
  • He is cooking.
  • I am making the bed.
  • The doctor is flying to California.
  • Everyone in class is reading.
• This verb tense is called “present continuous”, or “present progressive”.