Offering both Glitter Tats and Face Paint

So a question to those of you that do face paint and glitter tattoo parties... I am beginning to offer these as well and I have an idea of what I want to charge but not sure how to charge it. IE I offer one hour and 1.5 hour FP parties and I know how many I can paint in that time. So to those of you that do both for one party - do you add more time or just do simpler FP designs? Do you give the client the option to say? Or do you just bring the tats in the event some kids don't want FP?

I have it right now as both a stand-alone and an add-on to Face Painting but if I'm doing both for all kids at a party that's going to up my time and then I should be charging my hourly rate for that time plus the add-on price (for supplies and trouble) right?

I charge an hourly rate for the combo, but charge a bit less for tattoos. If I just paint for one hour (up to 10 kids), its 75.00, if they want tattoos, I add 60.00 for the tatts and the extra time. They are quick but still takes time with kids running here and there.

And I've found they are quick - but not THAT quick. Although practice is helping.

So basically you have a 2 hour minimum for that type of party and give kids both FP and a tattoo...