What does James mean when he says "Great, now we have two of them to look after"? How does Captain Keller react to this? Why is this surpising?

When Annie Sullivan arrives at the Keller home, Captain Keller is apprehensive.  He does not like that Annie is young and had been blind until recent surgeries.  He makes comments about her being from the North.  His wife, Kate, tries to reassure him.  They have a discussion about the topic, with Kate speaking positively about Annie and Captain Keller expressing his doubts.  Then James jumps into the conversation, saying, "Great improvement. Now we have two of them to look after."  James is referring to the fact that Annie was blind and that Helen, her new student, is blind and deaf.  He is also expressing his opinion that Helen is a burden to him because of her disabilities.  Captain Keller is annoyed by his son's comment and snaps at him, telling him to go "look after those strawberry plants."  This is surprising because James had been reaffirming Captain Keller's own doubts about Annie Sullivan.