Takes about 3 hrs one way from Genting to Johor Bauru. 1 stop on the way only (for washroom). And it goes from Genting to Johor Bahru only, then you need to change to another bus that will take you from Johor Bahru to Singapore.
There is also a coach service running from KL to Genting.
But Johor Bahru is like Shenzhen : very messy, you need to beware of pickpockets, etc. So not advisable to go to Johor Bahru if you go with 2 kids.
To me, Genting is similar to Macau, casino for adults, some mechanical playground for the kids. And don't expect the place to be very clean. Frankly, I don't like Genting, going there for once is more than enough. (I went with my niece's family n her husband is a gambler.)