Once the child is sitting on the potty fill a large bowl or small bucket with lukewarm or tepid water, place the new "potty" toys in the bowl and set the bowl of water in front of the child. On the floor if the potty seat is low, or if it's a potty seat that sits on top of the regular toilet, set the bowl of water on a TV tray or something that provides a step, in front of the child. When the child places his/her hands in the lukewarm water to play with the toys, if the child needs to physically go, they nearly instantly go potty (it's almost an instinctive type of physical reaction), then cheer, cheer, cheer! Give lots of praise, and if you wish to give some type of a treat, go ahead.
Let them play as long as they want, as long as they sit on the potty. When they are done playing, put the toys away for next time. This is really great because it makes it fun for them so they cooperate, it totally ends all power struggles, and also no more waiting and waiting for them to go only to have them go potty as soon as the diaper goes back on. They also feel good because they have immediate success. Potty training no. 2 was more difficult I found, that just came with some time and patience and them learning in their own space and way, relax, it will happen.
Do you want to know how I get this idea? It's kind of a funny thing, my husband used to be in the military and when he was young in boot camp they used to always play jokes on each other in the night by dipping the hand of someone who was sleeping, into a pan of lukewarm water, thus making the person wet the bed. It just seemed like a natural progression to use this trick for good use in the potty training area and it worked great!