Where is the passenger airbag deactivation switch?

It is not always possible to disable the passenger airbag and details will be found in the vehicle handbook. If the facility exists there will be a key switch in the centre console or dashboard and the ignition key is used to switch it off.

It is reckoned there is only one reason to disable the passenger airbag and that is when a baby seat or cradle is used on the front passenger seat. If the airbag cannot be disabled the baby must go onto the rear seat.

Impact Depending (ID) airbags.
With the Impact Depending (ID) system, you and your passenger are given effective protection proportionate to the severity of the impact.

Conventional airbag systems are unable to differentiate between a severe impact and a lighter one. When they are deployed, they are inflated to the fullest level, making the airbag as hard as possible. In a low-level accident, this is not necessary.
The intelligent ID airbags are equipped with a two-stage gas generator. In a more severe impact, they inflate to their fullest level with minimum time delay, providing maximum protection for the occupants. However, when the accident is less severe, they allow for a slightly longer delay before deployment, protecting the occupants with a more gentle inflation. Whatever the severity of the impact, the airbags ensure that neither the driver nor the front passenger contacts the steering wheel or instrument panel.
A special weight sensor in the passenger seat registers whether the seat is occupied or not. The system can thus differentiate between a passenger and a lighter object such as a briefcase. If the seat is occupied by a weight less than 12 kg, the front passenger airbag is not deployed, saving replacement costs following a crash and potentially leading to lower insurance charges. The front passenger airbag can also be deactivated using a key switch, when a child seat is fitted.
finding a kit to disable the airbag is not going to be easy,noone including dealers will sell or install them on any bimmer,
you could find a kit and buy individual replacement parts,but,i wouldn't recommend it,much less recommend switching the airbag off,personally,I would purchase and install a 5 point restraint that doesn't let the child move forward too much and pull the seat all the way back,the child will not be hurt that way,also in a low speed crash,bimmers dont fully inflate the bag,here is what one owner has to say on a forum about it,
I take my 3, 6 and 9 year olds for drives in my car. These cars are very safe, as is evidenced by my auto insurance premiums being only marginally higher for the Z3 than for my pickup and my wife's SUV. Of course we do have those vehicles for use in transporting the kids most of the time.

Several key things to keep in mind: use a booster seat so the child sits higher, to move the seat all the way back, and to not allow the child to lean against the door--you need to have adequate clearance there.

It's hard for me to believe a side airbag could be worse than hitting the door itself in a side impact--assuming the child is sitting a little away from the door to allow full inflation of the airbag before the child hits it

Disconnect the battery negative terminal.
1. Wait at least 90 seconds after the ignition switch is
turned off and the negative (-) terminal cable is
disconnected from the battery before starting the
operation.
(The SRS is equipped with a back-up power source, so
if work is started within 90 seconds of disconnecting
the negative (-) terminal cable of the battery, the SRS
may be deployed).
2. Do not directly expose the steering pad, front
passenger airbag assembly, center airbag sensor
assembly, front airbag sensor, front seat inner belt
assembly, seat position sensor, occupant
classification ECU, front seat side airbag assembly,
side airbag sensor, curtain shield airbag assembly,
rear airbag sensor or front seat outer belt assembly to
hot air or flames.

Hello, I'm not quite sure I understand your problem. The passenger side airbag is turned off with the same key it takes to start the vehicle. Just insert the key, push it in a bit and turn it to the OFF position. It should light up to alert you the air bag is deactivated.

Passenger side airbag deactivation lamp inoperative. You probably have a bad pass. lamp switch located under a/c vent on dash.

bottom of the center consol should have a light.

deactivation on airbags can only be done at the dealer on request where a key system will be in stall for you to deactivate when ever

You have a problem in the PAD (passenger air bad deactivation indicator) light. You will have to replace the PAD switch to correct it, you can not get the light seperate.

Passenger Air Bag Deactivation (PAD) Switch
The passenger air bag deactivation (PAD) switch:

• is located on the instrument panel to the right of the climate controls.
• contains a light emitting diode (LED) that indicates when the PAD switch is activated (passenger air bag disabled).
• allows the passenger air bag deployment circuit to be disabled using the ignition key.
• should be used whenever a child safety seat is being used in the front passenger seating position.

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Prove Out the System
Prove out the system means to turn the ignition switch from the OFF to the RUN position and visually monitor the air bag indicator with the air bag modules installed. The air bag indicator will light continuously for approximately six seconds and then turn off. If an air bag supplemental restraint system (SRS) fault is present, the air bag indicator will either:

• fail to light.
• remain lit continuously.
• flash.

The flashing might not occur until approximately 30 seconds after the ignition switch has been turned from the OFF to the RUN position. This is the time required for the restraints control module (RCM) to complete the testing of the SRS. If the air bag indicator is inoperative and an SRS fault exists, a chime will sound in a pattern of five sets of five tone bursts. If this occurs, the air bag indicator will need to be repaired before diagnosis can continue.
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Active Commands
This command allows the technician to verify operation of the air bag indicator, passenger air bag deactivation (PAD) lamp and chime. When the air bag output command is executed, the indicator, the PAD lamp, chime and the chime are activated simultaneously for approximately four seconds. All devices are deactivated automatically.