Poo and pee in context

This is something that students of English as a second language hardly ever learn, but it is really important if we speak in English to our children.

This is what I have found and haven't found:

'How often should your baby poop, and what should it look like? Most new parents don't know what to expect, and find baby poop quite surprising! It has so many shades and consistencies that even experienced parents may not have seen them all. This complete guide to baby poop walks you through the various types of baby stool and explains what's normal and what's not as your newborn grows, drinks breast milk or formula, and starts eating solids. You'll find out when not to worry and when it's wise to be concerned.'(www.babycenter.com)

'If your baby is straining to do a poo, it doesn't necessarily mean that she's constipated. Before long, you'll recognise your baby's particular grimaces and grunts as she works on her bowel movements.' (www.babycentre.co.uk)

So to do a poo (British English), or to poop (American English) is the action, the baby poop or poo is the 'object' and stool is the formal word to call poops.

Finally, I don't understand very well the use of pee and wee or wee wee. I have found that the most polite verb to use is to urinate, but which one is the colloquial one and how do we use them?. I need to ask this to a native English speaker as I can't find it on the Internet.