Weird? I don't know how places do things now a days..but 20 years a go I worked in and then was an asst manager of a Bally's Child Center. Free with the membership (with a 2 hour time limit per day). No tip jar. They make an hourly pay, I assume, that they agreed to (no one ever makes what they "want" for a job). Its not the same scale states set for based on standard tipping potential to add to it (again, I am assuming).
But, as a child care professional, I will take real offense to your "He plays by himself, so its not like they are doing much" statement. If he chokes..has a seizure, or some simple mishap befalls him, who is responsible for his immediate safety? Can you do that thru the TV screen? This is similar to the statements I see and hear from parents who say a babysitter or childcare should not be paid the same, etc while children are asleep, or because they are "older" and don't really "need care". OK, my rant is done now.
Personally, I would not be likely to tip, unless it was the holidays, etc. Who is reporting that income? I am a bit cranky about such things..altho I am a great tipper for standard tipping services!!!