Are tamper resistant outlets required in a cabinet with child proof latches?
In NEC 2008 Tamper Resistant receptacles are covered in section 406.11

406.11 Tamper-Resistant Receptacles in Dwelling Units. In all areas specified in 210.52, all 125-volt, 15- and 20-ampere receptacles
shall be listed tamper resistant receptacles.

Since section 210.52 specifies receptacles located within cabinets or cupboards, even those receptacles in the cabinet used to supply disposals are required to be tamper resistant.

210.52 Dwelling Unit Receptacle Outlets. This section provides requirements for 125-volt, 15- and 20-ampere receptacle outlets. The receptacles required by this section shall be in addition to any receptacle that is:
(1) Part of a luminaire or appliance, or
(2) Controlled by a wall switch in accordance with 210.70(A)(1), Exception No. 1, or
(3) Located within cabinets or cupboards, or
(4) Located more than 1.7 m (51.2 ft) above the floor

NEC 2011 revised section 406.11 to 406.12 and added some exceptions.

406.12 Tamper Resistant Receptacles in Dwelling Units. All non-locking type 15A and 20A, 125V receptacles in a dwelling unit (210.52) must be Listed as Tamper Resistant, excluding the following locations:
• Receptacles located more than 5 ½ ft above the floor
• Receptacles that are part of a luminaire or appliance
• Receptacles located within dedicated space for an appliance that in normal use isn't easily moved
• Non-grounding receptacles used for replacements as permitted in 406.4(D)(2)(a)

However, none of these exceptions exclude under cabinet receptacles. If you're replacing the receptacle under the cabinet or installing a new receptacle under the cabinet, it must be tamper resistant. Having a lock on the cabinet door has no bearing on the code.