Technically there are 5-6 types of IC in Malaysia and Mykad is just one of them or considered the most common most complete prove of citizenship. haha.

As for British family, they won't be eligible to apply for a Mykad unless one of the parent to the child is a Mykad holder. Let's say, your kid wants to apply and your wife is a Mykad holder then your kid might be eligible for Mykad if you and your wife is registered here as marriage couple.

Other than that you have to stay here for at least 5 years to get MyPR and after obtaining MyPR another 5-10 years to eligible for Mykad.

To not wait for so long and get instant resident status. You can apply for MM2H kad.

Maybe I am abit ignorant but can I know what is the advantage of having a PR or citizenship in malaysia? Why is it so important?