Its just an auto confirmation email to confirm that they have rcvd your email. Its always written in it that they will reply within 28 days. They usually reply within a week or less and oftenly in 28 days. Dont wait for their reply and start gathering the documents of new born like her Birth certificate, passport copy, photos, 150 cad processing fee,IMM0008ENU_2D form and additional family information form IMM 5406 for you and your spouse, updated proof of funds (may be) and proof of your residential status in UK. Please refer to the email I posted here on previous correspondence. If you are confused let me know or PM me, but dont wait for their reply. Gather documents to avoid any delay or rejection.
Regards.