Reduce the power.
A (massive enough) CPU core burns about 400W, and normal human operations require about 200 W. So let's start by reducing the waste heat to just one kW.
One kilogram of ice at -40 °C can harmlessly become one liter of water at 95 °C; that absorbs about 2 kilojoules per K to go from -40 to 0, and that's eighty kJ. Then a whopping 334 kJ is needed to liquefy the ice. Finally the remaining 95 K eat up 4.186 kJ each, for a total of 397 kJ. All told, that's around 810 kJ, or 810 kW*s.
You can hide your 67 kW of power for twelve seconds, or a more reasonable 1 kW for thirteen minutes.
If you can store five kilograms of ice inside the body, that's five time the endurance; but thirteen minutes ought to be plenty.
To be really picky, the child's body can and should already radiate about 80 W away to maintain a believable temperature.
You don't need to maintain a human temperature, you just need to fool a thermal imager. Thermal imagers usually ignore temperatures below 25 or 30 degrees (even if they are capable of detect the range, which not all do) to reduce visual clutter. For example, there's no way that the floor here is all at the same temperature. It can't be. But it's shown as black because it's below 24 °C.
So if you know this, and if the ambient temperature is, say, 20 °C, you can blow out air at a controlled 23 °C provided you're far enough from anyone else that they won't notice. The quantity of air you need to vent will be huge: at 0.55 kJ/K per cubic meter, and having only (23-20) = 3 K of deltaT, you can get rid of 1.66 kJ every thousand litres of air. Eliminating one kW requires 600 liters per second, or 21 cubic feet, which is a bit much.
Another possibility is to radiate the energy in some direction it won't be intercepted. Imagine the head containing a hollow cylinder, open at the top of the head, covered in IR-transparent fake hair and the bottom heated until it radiates in the near infrared. The cylinder also needs to suck air from the outside to prevent a heat plume becoming visible on the thermal imager. With a three square cm aperture you should be able to eliminate one kilowatt without problems, even if the ceiling will heat perceptibly. Moving around and looking all around, as children are wont to do, should be enough to spread the "heat ray" and avoid this; even if your android will need sensors to be sure never to "illuminate" anyone, since at close range the IR discharge would be enough to ignite paper and permanently blind.
Air cooling plus radiant heat discharge plus internal heat sump ought to be enough against the average scanner.
Frankly, I'd be much more worried of the metal detectors (due to the way they work, they will detect electromagnetics and non-ferrous circuits, and the only shielding possible - iron yoke or magnacloth - will both be readily detected).
(Also, terahertz-flash imaging detectors and facial scanners would probably react to the android's skin, but that can be prevented using a suitably complex covering for the android - same goes for skin texture etc. (NSFW link)).