I did this on the fourth level "Family home". Can be done elsewhere too.
When you start the level get Mike in the kitchen and switch to him.
The first cactus is beside the downstairs tv in the living room.
The second is beside the Wardrobe in the dining room with the pink Walls.
And the third is in the room downstairs across from there beside the pink piggy bank.
Finally head upstairs and grab the last one in the hallway up there.
Achievement unlocked, simple.