Be somewhat honest with the kid. Let him know you love chatting with him, but you're over sensory (or whatever your particular issue is at the time) at the moment and you can't give him the attention he deserves right now, but you'd love to hear about it later.
Kids are smarter and notice more than you think. Being honest and open about your issues is healthy for both of you, and helps show the kid it's ok to not be in the mood to talk to someone and a kind/polite way to disengage.
John Wick - Keanu
I would pay money to see that in theaters