When you (daddy) are out alone with your toddler Daughter, or (mummy) out alone with your toddler son, and needed to go toilet for the big one, (omg), what would you do?

I don't have a toddler, but I've ever needed to go to the toilet (big one). I just babywore her and did my business while she was screaming her head off. I had no choice but to attend to the more urgent need. There are baby carriers which can support toddlers, so the same thing can be done. Children up to the age of 6 can be allowed into changing rooms meant for the opposite gender in swimming complexes, so I would assume that it's the same for public toilets. If you don't want the kid to share the same cubicle, get him/her to stick his foot under the cubicle so you will know they are still there and not running around.