What quantities of chalk are harmful when ingested by 1yo.

[wookie]

Older ds loves sidewalk chalk while younger ds can`t resist eating some. I cannot look away for one second whitout him popping one into his mouth. How anal do I have to be with him and chalkÉ!

[seagull]

I would be careful because I once heard that some sidewalk chalk had lead in it. I don't remember the specifics of that though. Looks like that was from 2003.
http://www.snopes.com/medical/toxins/chalk.asp

I don't trust that it wouldn't happen again, so we are careful to wash hands after using chalk.

[zinemama]

Try calling poison control. They are great with that kind of question.