I just set them up and let them go. We offer crayon and markers at an early age. I can remember putting my oldest in the high chair with the wasable markers and just letting him go at it. I think he was about 1 maybe a little older.
I find most toddlers like to do what mom does. they are like little sponges soaking up everything. get your toddler to sit at the table after you have gotten everything ready for the project so they dont get bored waiting. tell them you need thier help as well, they love to help at this age, it gives them a sense of pride. when they complete something make sure to give lots of praise, they will want to do more.
Just get the stuff out. My son starts getting excited the minute I head to the closet that holds all the craft stuff. If keeping them engaged the whole time is a concern, have everything prepped before hand. Also realize that if they don't stay engaged that is alright. The point is to have fun,
Just keep offering craft activities. I will let my toddler have crayons and a paper and she will color for a few them go do something else, then go back to coloring. Maybe try finger painting, play dough, and things like that too. Put an old table cloth on the floor so they have room to play and clean up is easy and let them have fun, also make sure to join them!
Try messy things like finger painting (you can do finger painting with yogurt. Vanilla yogurt plus food coloring equals lots of fun!) My almost 2yr old made valentines cards this yr and it was hard getting him to focus on what we were doing. Mainly because he wanted to eat all the stickers. Lol I sit him in his high chair so he isn't running around while doing arts and crafts.