It wouldn't be deception if you tell him you have a surprise for him, it would just be a surprise.

[Honestly, she can't imagine Nero being angry; he's always appreciated it when she's gone to the effort to surprise him.]

The last time we spoke he said he had a surprise for me, I bet he won't be expecting me to surprise him.

[She's also quietly hoping that he'll be delighted that she and his father are getting on well enough to go to the effort to surprise him. It'll be a bonding exercise.]