Hun, your nephews are blessed to have such a fabulous aunt . Just be yourself and you'll all have a blast!! What more would they need?

Practically - as for the 2 yr old I'd find out his favourite toy, hobby, past time and use it to your advantage in case of melt down .
Once I get him away from his mum he'll be fine He picks up on her anxiety - last time we took them out, he was hysterical as soon as we got there because he knew we were taking them out. He screamed blue murder through us getting everything ready, installing the car seats, putting the boys in them, saying goodbye to parents, and driving down the driveway. The second we turned the corner, he stopped, like someone flicked a switch, and was fine the entire time we were gone. Theoretically I know they'll love the zoo, but I'm terrified of him melting down in public, LOL. I guess if he does there's not a lot I can do about it, I'm sure anyone around would understand

I usually take a little animal book with us to places like that. Then we look at the pictures with Moo, showing him what animal we looking for etc. Then when he starts getting ansty we pull it out & find the animals we've seen already.
Oh what a great idea, he has an animal book too!

Take 2 prams/strollers so they can rest... maybe even sleep! At that age I wouldn't spend too long at each animal, or else just plan a certain number of animals to see... don't plan on seeing the whole lot (depends how big the zoo is tho I guess).

I'm sure you'll be fine tho.. just take it as it comes.. it'll be fun!
They've got a double pram, toddler in front and baby in back, should work awesomely. And this time I'll even take it, instead of stubbornly declaring 'I'd love to hold the baby for 4 hours while chasing the toddler around Scitech', ROFL!

dont be anxious...they can smell fear just kidding
its the zoo you'll all have a ball
your a great Aunty by the way I bet your nephews think your awesome even if you do put them in rooms with smiley stickers