Final answer:
Henry sees his mother and his siblings Wendy and Peter when he walks into his home.
Step-by-step explanation:
Henry sees his mother and his siblings Wendy and Peter when he walks into his home. In the passage provided, it mentions that Wendy and Peter were at a special plastic fair across town, but they had called home earlier to say they'd be late. So Henry's mother and siblings were both present in the house when he arrived.