Have you applied for your spouse and children as accompanying dependant applicants?
You can land with your children first and your spouse can land later. However, the validity period of your visa is exactly one year from the date of the medical exam (or the passport expiration date, if that is earlier) and it cannot be extended. Your spouse MUST land prior to expiry or he/she will not be able to land at all and will have to come to Canada under some other program such as you sponsoring him/her, in other words you will start all over again.
If your spouse cannot come to Canada within a year of the medical exam, list hiim/her as non-accompanying, and you'll have to apply to bring him/her over later in a separate application.