S.H.
I am potty-training 2 2yo boys in my daycare. My criteria is: the child has to be self-aware of the need to go BEFOREhand.....otherwise it's simply a matter of the adult initiating the process. & because of this, quite often families have to stop/start the process multiple times before potty-training is a success.
Until the child show self-awareness, the entire process is delayed. I also believe that using pull-ups/diapers simply delays the process further. :)
In a perfect world, I wait for self-awareness. About age 2, I begin introducing the concept of using a potty. We read books about it, we talk about the older kids using the bathroom, & we discuss diapers/babies vs. big kids. In other words, I set the stage.....
When the child begins to tell me "after the fact"....then I begin encouraging recognizing self-awareness. For me, this is a process... which takes time. I am also very adamant about not allowing potty time to become a game or playtime. No toys, no books.....& we have to sit still. I sit on the toilet lid & wait for them. In other words, I "model" the desired behavior. :)
As for your concerns about the babysitter, ask her about her policy & methods for training. Try to reach a common ground in approach. I think my worst case was when the parents allowed the child to carry the potty chair all over the house....nope, no way, not in my house! With all of my families, I requested: sweatpants (no jeans), at least 2 sets of clothes, & extra socks/shoes. Until recently, I also requested NO pull-ups & used only the thick training undies & plastic pants. I have lightened up on that request now that pull-ups have velcro tabs. :) Hope this helps......