I think you need to go really plain and simple. White or cream is a great color for this (or something pastel from soft subtles).
- I would think flowers could be appropriate. Everyone has those, something classic (RIW, Toile?).
- Alphabet stamps could be used to put the child's name/initial (after all it is a naming ceremony).
- Religious quotes could be used for a minimalistic look.
Perhaps if you share the stamp sets you have we could come up with something.