Cardboard boxes are great to play with. You could decorate with them, trace their handprints, draw and depending on size can be used to store things in, sit in, make a cubby, the possibilities are endless.

Set up books . the hard ones to stand upright with teddies next to them. They’ll crawl or walk to them straight away.
tben sit with them to read one.

Put large paper cellotaped to cover table and give crayons to colour on paper while sitting on chairs.

Get can of shaving cream for two year old with tad colouring in it. Needs an apron on and supervision. Fun to play with in highchair or at table.

FILL up plastic lemonade containers with water and glitter and food coloured water. Glue on lids for them to shake them up.

Change around their toys about fortnightly so they dont get bored. they have renewed enthusiasm when toys look different. Less is sometimes more!

Make a craft box full of all different bits & pieces appropriate for their age. Colouring books, pencils, crayons, pieces of fabric, cardboard, paste, glitter, feathers, blank masks.
You can also make a garden with them outside & let them water & tend to it.
Vegetable gardens are good, they save you money & there is nothing better than your own fresh vegetables.

print some colour in sheets for them to colour in, baking, painting, blocks

my kids love drawing out the back with chalk, painting with water on the fence, “helping” me with housework, indoor cubbies, playing with balloons and empty boxes & colouring them in, storytime at the local library and lots of craft (we reuse lots of stuff like toilet roll holders, containers, catalogues)

i got a water table for my kids they love playing with it.

craft things my daughter loves to put pictures on paper

there are some good comments here

Craft!! Get a big box of random things… Kids love to cut, tear, glue, colour, touch and create things. This is the most exciting activity my kids can ever imagine!

The other day me and my lo made some home made playdo. I got him to dump the ingredients in and mix it all up. I of cause did the part on the stove he thought it was fantastic.
We also go for walks and look at all the different things to see and end up picking up leaves, rocks you name it then we get home and do some craft

Colouring in and craft as well as reading will entertain them for hours. Also bake some cakes or cookies and get them to help

colour in craft, painting, playdough,

Pack a picnic and walk to parks in the area. Park hunting. Meet your neighbourhood kids, organise play dates out of your area in park lands. Look in your kids magazines for fun things on for kids Sydney’s Child is great similar magazines available in other states. Beaches are fun go early or late and have Dad meet you there for a evening swim and dinner. Indoors there is ice skating for tot’s, playlands, indoor swimming centres and the library offers many different activities.

Provide them with a sensory activity (water play for bathing dolls, frozen animals in ice cubes etc) and let them decide what they want to do with it

I don’t understand why you as the parent need to keep them busy. I have never been one of those mums that organises activities for my kids. They used to play and entertain themselves with their imaginations. Yes I would have playdough etc but they would basically play with their toys and each other. They are now older and are always able to entertain themselves. I don’t think I have ever had them say I’m bored. I’ve seen too many ‘organised’ toddlers who when they hit older ages still want to be organised and so can’t play.

Pots and pans with dry pasta will keep them busy for hours

Bubbles! All my kids love them and my 2 year old and I play with them daily. I get the big bubble wands from Woolworths for $2, and have a bubble gun as well. We also have kinetic sand which is great and less messy than traditional sand and is a real hit here at the moment.

Play dough! They can be as creative as they like. You can make it together as an activity and maybe make different colours.

Use the shell water trays they are big enough to sit in, fill with water and bubbles and food colouring, they will love it

Do you let them do free play? My son is 20mths & at the moment other than playgroup with structured activities I just let him go free. They love painting, playdough or air dry clay, get a dress up box or little toy kitchen