THESE TRICKS REQUIRE NO SKILL
Just a bit of rehearsal, of course!
Though specific magic effects are not mentioned by name in the script,
most performances of Mary Poppins use some simple magic tricks
to visually illustrate Mary's "magicalness".
Some productions have Mary producing oversized plants or flowers from her magic bag.
This can be accomplished by having the bag placed on a secretly hollow piece of furniture,
like a radiator cover against the wall, or a dresser.
Mary opens the bag, reaches in and secretly lifts the bottom flap on the bag
so she can reach further into the hollow furniture and pull out the large item.
See this movie clip from YouTube.
The movie people used a masking system to make it look like you could see under the table.
Your production could just put the bag on a dresser or other "solid" piece of furniture- it will still look magical enough.
Some magical items to produce could include a Giant Appearing Straw, a Multiplying Bouquet, or even a Rubber Chicken for a laugh.
For the medicine scene, Mary could use the Airborne Sprite Can (with a label on the can to make it look like a medicine bottle)
to pour clear liquid into the glass.
Then she could dispense it to each child into their glass, with the liquid changing color.
The color change happens when the child's glass secretly contains a drop of edible food coloring on the bottom.
When the clear water hits the food color, the glass contains colored water.
In the Broadway production, there was a lot of flying going on.
Most likely your production does not have the budget or expertise for that.
To make your own magical levitation moment, your actor can do a simple optical illusion.
Here are instructions for TWO simple methods you can use to create this illusion.
BONUS VIDEO: Get exclusive additional ONLINE instruction with expert tips from Peter Monticup!