In real heat, as little as possible: a short-sleeve bodysuit and a sun hat, bare legs and bare feet, and shade.
For a baby of 6–12 months on a still, dry day:
25–35°C (77–95°F): short-sleeve bodysuit and sun hat. Hot — as little as possible, plus a sun hat and shade.
Overheating is the risk for a baby in hot weather. The NHS says never to cover a pram with a muslin or blanket, because it traps the heat. Shade and water matter more than any garment.
Under six months, keep your baby out of direct sun altogether.
Each piece comes on at its own temperature, a degree or two apart, so the outfit changes one piece at a time.
One light layer from 20°C, covered arms below.
A sun hat from 23°C, or from 20°C in sunshine.
0–3 months, 28°C: short-sleeve bodysuit and sun hat. 3–6 months, 28°C: short-sleeve bodysuit and sun hat. 6–12 months, 28°C: short-sleeve bodysuit and sun hat. 1–3 years, 28°C: T-shirt, shorts and sun hat.
Still and dry: Hot — as little as possible, plus a sun hat and shade. Windy (feels like 25°C (77°F)): No change Raining (feels like 27°C (81°F)): No change Sunny (feels like 30°C (86°F)): No change In a carrier (your warmth counts on the body): No change In a car seat (no coat under the straps): No change
Never cover the pram with a muslin or blanket in the heat — it traps the heat.
Check the neck — warm but not sweaty means just right.