M.R.
The glue is fine, not sure that 18 month olds would get too much out of this activity, there could be something more appropritate, but they can't get hurt that way, and this would be one of those things where YOU would be doing the craft for the most part anyway.
If I could offer you a little Old Mama advice...lighten up, he is going to be fine, you may worry about every little thing it is not good for either of you! There is so little that you can do that will really harm him and the world is a wonderful place, don't take him home every time something new comes along or he will miss a great many opportunities. Language development in an enriched enviornment is huge right now, and even if he could not really do the glueing, you could have said so many new words and he could have seen and felt new things that would have been totally amayzing to him. Let him experience life! He will be just fine (even if he eats a deli meat occasionally or a little glue occasionally!)
God bless Mama, you are doing fine, give yourself permission to enjoy the world-you made it, so will he!
M.