My children have a board like the picture 1 above and there are some flat wooden pieces in the shape of animals like the picture 2 above.
There are some holes in the board and the children will put the correct pieces into the holes.
Do we call these holes "holes" or "gaps"?
or can we just say "the children can do the picture jigsaw"?
Those are holes or spaces.
A "gap" is a complete separation in something continuous, like a number line with a number missing, or a wall with a space to walk through. But the holes in your picture don't separate the yellow surface as it's still connected around the hole.
I'd probably call them "empty spaces", but "holes" is OK, too. A "gap" is usually in one dimension (e.g., a gap in a row of people or in a timeline), but it would certainly be understandable in this context, too.
Yes, we can also use the verb "do" (although "jigsaw puzzle" usually refers to a different kind of puzzle):
The children do the puzzle.
However, "do" is very vague, so a verb like "work on" or "complete" would probably sound better in most contexts.
