We live in a hot climate so have got used to managing this one! Hope some of our ways help:
sleep at night in T shirt but bare legs, T shirt soaks up any sweat therefore avoiding getting chill, and is still nice and cool
bare feet where possible especially if there are cool floors to walk on
ice lollies made from frozen fruit puree, especially ones made in layers so they are stripy
lots of water, keeping really hydrated helps the body´s natural cooling mechanisms. drinking lots, lollies if all else fails, but preferably without refined sugar in as sugary drinks and lollies make you thirstier. Give drinking water at room temp if poss, as really cold water from fridge actually passes through the body more quickly without staying long enough to give hydration (plenty more wet nappies, but no water staying in the body)
fan in the room, pointed at the wall, as directly on little one can cause chills, but blowing towards the wall diffuses the cool air more effectively around the room
paddling pool under a sun shade! tepid baths in the evening (water at body temp is much more effective at cooling than cool water, which makes your body react in a way that actually warms you up)
use cold foods as snacks, eg cherries, cherry toms, cold yogurty dips etc all kept in a cold fridge
a layer of loose fabric is better than bare skin as it helps air to circulate around the body, so a loose cotton dress is much better than a strappy sun top
When it gets really hot, encourage sleeping during the hottest part of the day. Might skew normal bedtimes for a while, but it may be easier to have the activity time of the day when it's cooler anyway
Um, think that's it!! Hope it helps