
Puzzles happen to be a lot of fun and essential activity for child development. So they say, and I believe they might have a point. Each child develops at his/her own rate. So, it is not easy to know when exactly to introduce these activities... we let Ana guide us mostly.
Once baby knows to sit up steadily and has enough dexterity to pick up food and other toys items intentionally and place them at a different spot with certain premeditation, as well as have enough focus to recognize patterns, it seems like a good time to introduce the puzzles. When Ana could recognize animals, shapes, fruits and such, around 15 months, we introduced what I call Stage One puzzles pictured above.
I call these Stage One for these reasons:
1. easy for baby hands to pick up using the little plastic knobs (caution: never let the child do it unsupervised at this age - they tend to put things in the mouth and these little plastic knobs are a hazard); and if it doesn't have the knobs, the pieces are large enough to be held by baby hands comfortably.
2. easily recognizable shapes for the puzzle pieces (unlike jigsaw) like animals or fruits and only one would seem right - not a lot of ambiguity.
In the picture above the farm animals puzzle (Melissa & Doug™) was a favorite as Ana used to love stating the animal name and putting the right piece in the right spot. All wooden shapes are the same in this farm animal puzzle, but for the color and pattern which helps identify whether it is a sheep or a horse or a cow or a duck...
Next is what I call Stage Two puzzles:

These don't have knobs for easy pick up, but, have large enough pieces, not quite jigsaw, that will only fit one way, no ambiguity. But, it is a bit more challenging as the shape of the pieces are not uniform or easily recognizable. For instance the Peanuts one in the picture or the Pluto one, all the kid has to know is where the head and feet and such goes and then try to assemble them such that the pieces fit. But the challenge is in the fact that it is not easy to put certain pieces in place before the others are in place. Between 18 and 24 months, Ana seemed to like these.
Next are what I call Stage Three:

These are basic 9-piece jigsaw puzzles with very open and simple themes. Ana loves the animals one - with dog and cat and goldfish and bunny and such. In this category, slightly more challenging 9-piece is the abstract one of the multicolored elephant puzzle in the picture - which is actually 2-in-1 where front is a single elephant and rear is many elephants - aimed at introducing
one and
many - but the picture is abstract enough to be challenging, yet, easy enough as there are only 9 pieces and only one way they will fit. Around 22 months, closer to turning two, Ana started to focus her attention on these jigsaw puzzles which have a general overall pattern, but the individual pieces don't always seem to make sense.
In my mind, Stage Two and Stage three overlap. They seem equally challenging and interesting.
Next are the Stage Four:

These are more challenging 24-piece jigsaw or block puzzles. Ana is about 27 months now (2 yrs 3 months) and she is into these. The block puzzle is actually 6-in-1 "farm cube puzzle" where 16 blocks need to be assembled in proper order to complete each of the six puzzles.

My favorite puzzles for Ana so far have been Melissa & Doug™ wood puzzles. However, some of the ones in the pictures above are possibly 30 years old as they were gifts from my mum-in-law - apparently D, my husband (her son) used to play with them when he was little! I love the fact that she held on to those and passed it on to Ana.
What usually worked with Ana is, I used to set one puzzle out at a time - all jumbled - in her play area, very handy and at a convenient spot for her to find and assemble them. In the middle of playing with her toys, she would notice this and start putting it together and scream when she gets frustrated and needs some gentle direction or nudge.
By no means am I an expert in child development activities, but, I wanted to share some of the puzzles Ana has enjoyed doing since she was about 15 months or so. Perhaps children are ready even earlier and we can let our children guide us...
This post is completely inspired by Sandeepa's thoughtful comment left on one of my posts. Thank you Sandeepa for giving me an opportunity to share one of my favorite activities with my baby.