Petronas towers, garden behind the towers (think it's the KLCC park?) batu caves, the Islamic arts museum is stunning and my kids enjoyed it.

We started at the butterfly farm. It is pretty good. Lots of butterflies (although not as many as other ones I have been to. They were not landing on us or anything), a few fish ponds where we could feed the fish and some random tanks with things like turtles in them. It was a decent size and a nice place to wander around. At the end, there is a whole lot of exhibits inside showing lots of insects and creepy crawlies.
The KLCC playground and water park is amazing – and it’s free! It’s a giant playground with lots of different play areas suitable for all ages. There’s also a shallow wading pool with a waterfall that’s perfect for the dc to cool off from the heat. If you’ve got jet lagged kids and are up a bit later, then watch the nightly water fountain light show that takes place outside the shopping mall next to the playground. It’s quite a fantastic sight and our kids loved it.
The discovery centre (basically a science museum) is great. There are so many hands on educational exhibits. Both kids loved it. Adults are RM25, 3-12 year olds are RM15, kids under 3 are free.
Berjaya Times Square is a good place to escape the heat. Even within the shopping centre there are lots of things to do with dc. They also have some cool random stuff, like “piano stairs” and we enjoyed going to the cinema – so much cheaper than here.
The Lake Gardensaka Kuala Lumpur Perdana Botanical Gardens is a fantastic place to have a picnic and play games under the shade of a tree. Entrance to the gardens in free.
Public transport in Kuala Lumpur is excellent, so it’s easy to jump onto the train and head out to the Batu Caves. Bring your walking shoes because it’s a climb to reach the entrance. My Dc loved wandering around inside and they also loved the monkeys that play around the stairs and entrance to the cave, but be careful not to bring any food with you as they’ll snatch it off you in a second!

Honestly Batu caves is a downer- a Malaysian friend told me but I believed the internet give it a miss.

The KL Tower is worth a visit. I wouldn't recommend the zoo at the bottom though.

It has fluffy rabbits... and lots of hungry snakes.

Don’t bother with the deer park they only had 3 deer.
There are some lovely parks, a rainforest 8n the middle of the city.
Them big tower things
Hop on hop off bus will take you everywhere you could want to go.
River of life has light and music show at night.
KFC - is probably the best You’ll eat anywhere in the world.
Markets and China town.

KL Bird Park is amazing, it's not too crowded either (less crowded than the aquarium). Best to get there fairly early when its cooler.

China town is not fun to walk around, its hot and there's nothing interesting there (maybe a few temples but if you want to see temples I'd recommend getting a Grab to Thean Hou, much bigger and more impressive). If you want to go shopping go to Central Market which is inside, air conditioned and has nice souvenirs. Petaling Street is full of junk.

Lots of good suggestions. My favourite part of KL was the transport system, it’s so efficient. The train/ tube system will get you about seeing a lot.

I found it way too humid and hot when my family and I went two years ago. We stayed in kl for 3 days and went to the aquarium, klcc, twin towers sky bridge walk, little India,China town, the main square (can't remember the name), the lark behind klcc, the national mosque and islamic museum..

Eco Forest by the Memara KL Tower. It's free and all high rope bridges amongst the trees over looking the city.
China Town and also Kwai Chai Hong in Chinatown is well worth a visit (free) for the street art and good photo opportunities.
Thean Hou Temple is very pretty.
I liked Batu Caves. We've been twice on an evening - after 6pm. It's not very busy at all. By 7pm all the street vendors, coach trips, cruise tourists are gone. Both times I would say maybe 20 o 30 other people there ( and even less nearer to 8pm)and it's big so not crowded.