It may costs no more than 300HKD from the airport to Kowloon area. You can take one taxi instead of taking airport express, for the express airport line costs 90HKD per person. The cheapest way is to take airport bus A21, 33HKD per person and the children pay at the half price. If you need to use public transport very frequently, you can consider to buy the card. Recommend you buy ordinary types of card (not the three-day card including one way or round way airport express). Ordinary card can be used to pay bus fare or phone call and buy things in stores.
From the hotel to disneyland?!Take Bus 7 at the other side of the road to YMCA to Yau Ma Tei, then change to Tsuen Wan MTR line to Lai King to Tung Chung Line to Sunny Bay then change to Disney special line to disneyland. Ask for the clerk of the hotel, they are pleasuer to help you nay questions.