my 18mth old is number 4 child so he also learns fast, he loves playdough but i have to watch him incase he tries to eat it which he hasnt yet. He loves playing with match box cars and hide and seek. Because of his sister he loves tea partys. Hes starting to do puzzles but needs help with it. Have you thought about playgroups they have them in most areas normally at kindys.

At 18 months they love to bang on pots as the previous answer states.  I used to find a conainer with a lid and fill it with various items around the house.  These were small things but nothing that was too small and would be a choking hazard.  Things like a paint brush, a garlic press, an old address book, clippings of a photo that was trimmed for a scarpbook, ball of yarn (watch because the can be a strangulation hazard), a small toothbrush, a bookmark with a pretty picture, old credit cards or your old drivers license, etc.  They love to take the items out of the container, explore the new textures, colors, etc and then retun them to the container.

There are also the larger crayons and some special markers made by crayola that are ideal for the tiny hands.  Just put some newpaper under the work area and let them have a great time.

Have fun!

AN 18MTH OLD IS VERY INQUISITIVE. THEY ARE GETTING INTO EVERYTHING AT THIS AGE.  WHEN MY GIRLS WERE AT THAT AGE, I WOULD HAVE JIGSAW PUZZLES, BLOCKS, SHAPES AND BOOKS THAT POP UP FOR THEM TO PLAY WITH INDOORS.  I WOULD ALSO MAKE UP GAMES FOR THEM LIKE THE ARROW GAME.  I WOULD CUT OUT ARROW SHAPES OF PAPER AND COLOUR THEM IN 3 DIFFERENT COLOURS.  (MY 6YR OLD LIKED PURPLE, MY 3YR OLD LIKED RED AND MY 18MTH OLD LIKED YELLOW).  THE GIRLS WOULD HIDE IN A BEDROOM WHILE I PUT THE ARROWS ALL AROUND THE HOUSE.  THEN THEY WOULD FOLLOW THEIR PARTICULAR COLOURED ARROW UNTIL THEY FOUND THE LAST ONE AND I WOULD GIVE THEM A SURPRISE WHEN THEY BROUGHT THE ARROWS TO ME.  THE SURPRISE WAS USUALLY A BOX OF SULTANAS OR A WHITE OR CHOCOLATE FROG.  SOMETIMES IF I WAS BUSY, MY6YR OLD WOULD PLAY THE GAME WITH HER SISTERS.  THIS GAME KEPT THEM BUSY FOR AGES AND ALSO HELPED THEM LEARN THEIR COLOURS.  YOU COULD ALSO TRY IT WITH DIFFERENT TOYS OR BLOCKS ETC. GOOD LUCK.

Baby jigsaw puzzles, colouring books or drawing, play dough,  music making (banging pots, pans, bowls, etc), blocks, or activity toys. The way to keep him interested is for you to do it with him. I found with my 2 that age didn't allow me a lot of "play by themself time".