Sentence:  ... no man knowes whether a Wife and a Mother, which had such a latitude of power over the Father and the Sonne, would not be <WSD>tampering</WSD> with a Prince (even in the point of Religion) of so tender years as rendred him fit for any impression, and to be indoctrinated with such principles as well concerning Religion, as others best suitable to her own designes. 
Meaning of the word marked with <WSD> tags:  To try to influence someone, usually in an illegal or devious way; to try to deal ("with" someone).