Was thinking how to spice up our pancakes and eggs for the little ones and remember seeing pancakes in various shapes before. Do people put them right in the pan or bring them out and then cut them after they've been already cooked? I was thinking the same possibility for eggs too. Then I got to thinking whether or not it was safe to put them in the pan. Let's assume I have cheapo dollar store shapes and not the higher end stainless steel ones.
In general places that do this with pancakes do not cut-out, but indeed use a mold or the like. The scrambled eggs would likely look fine "cut", but part of a pancake is the edge, even if it is modified by touching the edge of the mold.
So long as the mold is metal, your dollar-store purchases should be fine.
You will likely need to oil/butter them in some way so that the product - batter or egg - does not stick to the metal itself.
I have myself used clean old tuna tins to make round "self-contained" fried eggs for a home version of a McMuffin.
I'm not sure that putting anything plastic from the dollar store in a hot frying pan is a good idea. Not only will they probably melt (which may ruin your frying pan), they probably also contain BPA, which is released when plastic containing the chemical is heated. That may or may not be a problem for you, but either way I would suggest just getting some cookie cutters off amazon or something instead.
Edit: I did some quick amazon searching and saw that you can get the Fox Run Dinosaur Cookie Cutter Set, Fox Run Marine Life Cookie Cutter Set, and Fox Run Farm Animal Cookie Cutter Set (all metal) as a combo for $19.93. If you're looking for cheapness, that works out to ~$1.10/cutter, which really isnt bad. Hell, I'm technically an adult now and I'm tempted. Dinosaur shaped pancakes/cookies/whatever I can cut with those would be awesome.
Don't use plastic ones for heating! I am not even sure about cheap metal ones. I have used Wilton's cookie cutters with the nice rubber grip; they work great! Get them with 40% coupon or after season sales :) I like them because you have something to hold on to even when the metal is hot.