In preschool age, it is not so much important that children absorb any specific knowledge, but that they accumulate practical experience. They will be able to use this experience later, when their brain develops and is ready to perceive theoretical knowledge.
For example, you can conduct simple experiments with your child with floating and sinking objects. Explain to him that objects that float on the surface of water are less dense and weigh less than water in the same volume. And those that sink, on the contrary, are denser and heavier. There is no need to go into detailed scientific explanations. The main thing is to give the child the opportunity to gain practical experience. And theoretical knowledge will come later, when his brain is ready for it.
This approach is applicable to many children's games and experiments. If your child asks “why?”, answer briefly and clearly. The goal is not to overload the child with information, but to provide useful practical experience on which theoretical knowledge can be built in the future.