What do I think?
I think that you don't have to lie in order to get someone to go to a suprise party! Your mom or dad could just have said that "We are going over to such and such a place let's go". If you asked them why are we going - they don't have to answer just encourage you to "hurry up".
Did your parents sin in lying to you? Yes - but I think their ignorance and good intentions - just like Rahab - is what God honours - not the sin itself which is forgiven in Jesus.
I hope this answers your questions and I hope you are not mad at me!
Your brother in Jesus,
Rob