This conjecture was advanced by Dowden in his edition of Hamlet for the Arden Shakespeare, 1899, p. 34, note to l. 109:
Does this mean, You will present yourself to me as a fool? or, You will present me (to the public) as a fool? or, can “fool” mean an innocent, a baby?—for Polonius is not over-delicate in his warnings. See Romeo and Juliet, i.iii.31 and 48.
Here's the passage he cites in support of this conjecture:
When it did taste the wormwood on the nipple
Of my dug and felt it bitter, pretty fool,
To see it tetchy and fall out with the dug!
Shake quoth the dove-house: ‘twas no need, I trow,
To bid me trudge:
And since that time it is eleven years;
For then she could stand alone; nay, by the rood,
She could have run and waddled all about;
For even the day before, she broke her brow:
And then my husband—God be with his soul!
A’ was a merry man—took up the child:
‘Yea,’ quoth he, ‘dost thou fall upon thy face?
Thou wilt fall backward when thou hast more wit;
Wilt thou not, Jule?’ and, by my holidame,
The pretty wretch left crying and said ‘Ay.’
To see, now, how a jest shall come about!
I warrant, an I should live a thousand years,
I never should forget it: ‘Wilt thou not, Jule?’ quoth he;
And, pretty fool, it stinted and said ‘Ay.’
But fool does not mean ‘innocent, baby’ here—it is an epithet applied to an innocent. One might as well argue that silly means ‘baby’ because mothers occasionally call their children ‘little silly’.
As Dowden says, the pun would be in character; and certainly both Shakespeare and Polonius are capable of layering their puns three deep; but I have difficulty conceiving that this meaning would ever occur to an auditor without prompting by an editor. The best that can be said of this conjecture is that it is ingenious, but unsupported by any real evidence—and I doubt Dowden himself would have claimed more than that for it.