I think the child’s arms burning in this film came from the father working incinerating garbage…updating

What's In Kay's Mind?: I found hands being burned by scalding hot water – Final Destination 2…

…his arms got burned in the metal opening.

Bad Seed figures into it.

“I thought God was punishing me”…  My mother spilled hot oil on her leg – wax museum?   Child stuck their hand into the hot wax by mistake?

The little girl didn’t steal the pen.