Sit on the floor when interacting with them. Literally being on their level can help a lot, that and talk about stuff they are into.
As someone else mentioned, don’t baby talk to them, unless they have some specific learning disability, a 5yo will know a lot about what they are into (a dinosaur kid will know heaps about dinosaurs)
My boys all love Lego, build cool stuff, then let them have it, don’t use instructions.