When I started my very first NP job last summer (in peds) I made myself a card that I laminated to keep in my planner. I used the most commonly prescribed meds and appropriate dose for each weight range in pounds. So for Amox, I had from xx-xx lbs get 1 tsp of 400/5 bid, xx-xx get 1 1/2 tsp, etc. (sorry I am just being too lazy to refigure the weights! I calculated amox, augmentin, azithro, bactrim, and omnicef. For amox I just estimate the weight in kg and if it is a bit higher, I just use the 80mg/kg (remember high dose amox is 80-90kg so you have some wiggle room). So for a 35lb kiddo, I just estimate 17kg x 80mg= 1360 (1 3/4tsp bid) rather than actually figuring 15.9kg x 90=1431 (1 3/4tsp bid). Just remember that peds doses max out at usual adult doses (my first day I prescribed Amox 400/5 3tsp bid-luckily the pharmacist called to tell me that was too much!)
I agree with the others. I have never had a parent complain or even look concerned when I say that I need just a second to double check my math as I want to make extra sure I am giving the appropriate dose, etc. Actually, at my peds clinical in school, the NP carried a planner with her prescription pad and a multitude of resources. I have done the same and take my day-timer with pda, scripts, and some references I use. My favorites are comparisons of low, medium, and high dose inhaled steroids by age (I think it is from the Fitzgerald review) and a comparison of strength for various topical steroids, etc. I also have the two sided Tylenol/Motrin dose chart as I always review proper dose with parents at the WCC.
Good luck and I bet once you stop being stressed about taking the time you need to perform the calculation it will seem easier!