Thanks for your reply.
Your fiance is in the UK as an EEA member state national I assume due to his Austrian citizenship/passport.
This means that once you are married you will have to apply for an EEA Family Permit. You will have to apply for this before you travel and and must submit the appropriate documentation to the UK embassy closest to her:-
You will see there is a link at the bottom of the page to how to apply. This contains details about supporting documents and the application form. Your child will have to be joined with you in the application as your dependent.
100% of such applications are determined within 40 days, but they frequently take less longer.
Once you are here on your family permit you will will be eligible to apply to the UKBA for a residence card which confirms her right of residence in the UK on the basis of your marriage:-
It will either take the form of an endorsement in your passport or as a separate immigration status documents confirming your right to reside here for 5 years.
At the end of this time your will be able to apply for a Permanent Residence here if you wish subject to the residential restrictions in place and the requirement that you are both still in the UK exercising treaty rights (ie. working).
You will be permitted to work as soon as you are here on the family permit.
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