I'm on peds right now and the residents taught me the 4-2-1 rule for maintenance fluids. For the first 10 kg multiply each kg by 4, for the next 10 kg multiply each kg by 2, and beyond that multiply each kg by 1.
Example: 25 kg child.
10 x 4 = 40 mL/hr
10 x 2 = 20 mL/hr
5 x 1 = 5 mL/hr
Total = 65 mL/hr
Hope this helps.