Of all the public attractions I've been to in Kansai so far, I must say Biwako Valley's child-friendliness should receive 5-star rating. If you're from a tropical country like I do, AND having to bring along 2 small children, what you want to look for in a winter experience is not to ski or snowboard (let's face it, there's a slim chance that you could master ski/snowboarding in a short amount of time to truly enjoy the sport) but rather a place where you can simply play in thick snow and go sledding with the kids. Biwako Valley is the perfect place for just that. Here's the link to an e-brochure of Biwako Valley (in Japanese)
Source: Biwako Valley
As far as I am aware, this is the only snow attraction in Kansai that has a children play area. A HUGE children play area that provides enough fun even for adults. They carefully separate the place to include snowman/snow ball playing area, a carousel and sledding area complete with an escalator. Shovels, snow ball making tools, sledges and toboggans are provided enough for everyone so you don't have to bring your own. The entrance to their Snow Land costs 500yen per person and free for kids below 3 years old.
Their restaurant is reasonably priced for a public attraction such as this but we brought our own snacks and eat at a rest area provided near the Snow Land. The rest area has a space for people to lie down where they even installed a hot carpet but you might have to come very early to book a spot. Lockers are available but being a penny-pinching gaijin that we are (:p), we just put our bags on top of the lockers instead and our stuff were still safe from theft.
Based on the reviews I've read, Biwako Valley is rather pricey compared to other ski areas in Japan. But for clean toilets installed with seat warmers and washlets, I really don't mind paying the extra. Moreover, all toilet areas are equipped with changing tables and they even provide a nursing room at the rest area. The place is well known for its great view as it looks over Lake Biwa.
Biwako Valley is easily accessible by public transport. Take the Kosei Line (湖西線) to Shiga Station (志賀駅). An then take the Keihan Kojak Bus straight to Biwako Valley. If you're coming by car, a per-entrance fee of 1000yen is charged for parking. Shuttle bus is available to take you from the parking lot to the ropeway/cable car station. You can print out this coupon from their site to get 300yen off on their round-trip ropeway ride. The coupon can be used for up to 5 people. Normal price is 1800yen for adults, 900 yen for elementary school children, and 500yen for preschoolers.