Hi Leash, congrats on the ceremony!
I just did a bit of research and did a google search on wedding invite no gifts. It came up with a few links that may be helpful. Also try a search on wedding invitations. This may come up with heaps of wording ideas.

If your ceremony is going to be 'low key' then I wouldn't stress too much with ettiquete and proper wording. Just say it like it is.

I love wedding and party planning so I will keep searching and hopefully find stuff for you!

PS- Just a quick story. On the day of our wedding my DD (then 3) just had her hair braided beautifully. I was getting photos taken and the limo had just pulled up when she came in with red lippy all over her face, her hair cut and nail polish all over her dress! Lucky your little girl is too young to get into any mischeif - hopfully.