Kiahuna Plantation or Poipu Kai

Cons / What to Watch Out For:

• Many (or most) units do not have full air conditioning. Some units have only fans, louvers, or very minimal “cooling,” which means in humid or wind-less periods condos can feel warm to hot.
• Because the pool/athletic-club facilities are across a street from the condos (not on the same grounds), using the pool or amenities may require walking/driving — less “resort‐hotel convenience.”
• The quality of individual units varies widely (some are updated, some are dated) — you may get a great unit, or you may end up with quirks (outdated décor/appliances, noise, broken items).
• If your family is sensitive to heat or humidity and expects “hotel-style” comfort (especially at night), the lack of reliable A/C can be a serious downside. Many reviewers with heat-sensitive family members found it difficult without A/C.

Poipu Kai Resort (Kahala / Manualoha) — Pros & Cons for Families with Tweens/Teens

• Pros: The location tends to be nice and central within Poipu, often offering short walks to beaches (e.g. Poipu or Brennecke’s), pools, and local amenities (restaurants, shops). Several units report comfortable layouts, well-stocked kitchens, and good proximity to beach + pool — nice for a family staying in and out.
• Some units apparently do offer A/C (at least in the bedroom), which helps if heat/humidity is a concern — this can be a decisive factor for comfort, especially if your family is sensitive to warm nights.
• Good mix of condo-style living + improved amenities compared with older “plain condos.” In larger or updated units, families have appreciated the space, washing-machine/dryer, and convenience of “home-like” stays without compromising on proximity to beaches.

Cons / What to Watch Out For:

• Even in units with A/C, often only the master bedroom is air-conditioned; other parts of the condo (living room, lofts, second bedrooms) may remain warm or humid. Families often note that living areas get “hot in afternoon” unless windows are open, which may not be enough on stagnant days.
• Because of partial A/C, sleeping arrangements for teens (if not in the air-conditioned bedroom) may be uncomfortable — e.g. lofts or pull-out beds upstairs may become very warm.
• On some hot or windless days, the ventilation / fan-only cooling may not be enough; some guests found that portable A/C units or more robust ventilation were necessary — which means you might have to request special units ahead of time.
• As with any condo-complex with individually owned units, quality and upkeep vary from unit to unit — so it’s important to double check the exact unit’s amenities (AC, layout, proximity to beach/pool) when you book.

Air Conditioning — Is It “Necessary” for December?

Because you're planning for December, air conditioning may be less critical than in summer months (temperatures tend to be milder in the Kauai south shore during winter). Even so — since your family is sensitive to heat — A/C or at least a well-ventilated unit may still matter. Some guest-reviews of both properties indicate that, in December, breeze and fans could be sufficient.

Given your sensitivity, the safest approach is to choose a unit that explicitly states A/C is available (ideally whole-unit or living-area + bedrooms) rather than relying on open windows or fans. On Poipu Kai side, you’re more likely to find at least partial A/C (often in master bedroom) — but it's not guaranteed for the whole unit. On Kiahuna Plantation, many units have only fans and no A/C at all — so unless you find a rare updated unit, you risk uncomfortable nights.

Which Is Probably “Better” for Your Situation (Family with Tweens/Teens, Sensitive to Heat, Visiting in December)

Based on what you’ve told me — I lean toward recommending Poipu Kai (Kahala or Manualoha) over Kiahuna Plantation — but with the caveat that you must carefully pick a unit with A/C (ideally more than just the master bedroom). The convenience of pool + beach nearby, the possibility of A/C for cooler sleep, and a condo-style unit you can walk to beaches/pools from — seem to better align with comfort + flexibility for a family with tweens/teens who may want a mix of beach, pool, and exploring.

Kiahuna Plantation would be a more budget-minded option and could still work if you prioritize beach-front access, cooking your own meals, and don’t mind relying on breezes/fans — but it feels riskier given your stated sensitivity to heat.

My Recommendation If I Were You:

• Focus your search on Poipu Kai units that clearly list A/C — preferably with reviews confirming the A/C works and cools more than just the master bedroom. Ask the property manager directly about airflow, ceiling fans, and typical nighttime temps.
• If you lean toward Kiahuna Plantation only because of cost or kitchen/condo layout, only go for a unit that recent guests say had A/C — otherwise plan for possible discomfort (or bring portable fans).
• Because December evenings are often milder, even fan-based cooling may be manageable — but to be sure your family sleeps well and isn't irritable from heat, A/C is worth prioritizing.

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