COVID-19 can spread in all age groups, as mentioned in the first statement. However, older individuals and those with pre-existing medical conditions are at a higher risk of developing severe illness, as stated in the second statement. On the other hand, the infection tends to be milder in children, as mentioned in the third statement. Therefore, all of the above statements are correct, indicating that COVID-19 can affect individuals of all age groups, with varying levels of severity.