This is meditation in action, the discipline of daily life. Trungpa says to continue the experience of meditation in your daily activities, remembering that all this stuff that seems to be going on is, at least as understood on the absolute level, just an illusion created by your mind-system.
Remember to keep everything soft, pliable, workable, with lots of space. Recognize the simplicity of the phenomenal play.
The phrase “child of illusion” has always been hard for me to understand. My best take on it: – it suggests that you – that notion of ‘self’ that is identified as ‘you’ – are created by (child of) the illusion of experience. To ‘be’ that, perhaps, means you recognize it clearly.
Yes, this one is a bit confusing, unclear perhaps. As I understand it, the “be” means just being aware of this truth. The “child of illusion” is the Self. The essential notion is that the Self is not a fixed, permanent entity, and keeping that in mind as you go about your daily life helps to lighten things up a bit. The self, in the Mahayana and Vajrayana traditions, is understood to be simply the product of stringing together all these discrete experiences of ongoing life and reifying the experiencer as some entity, “me.” Of course, since all this stuff going on is essentially created by the mind, it is an illusion, so its creation, the Self is also unreal, in the absolute sense.
Judith Leif says, “In this slogan, the particular postmeditation practice is to “be a child of illusion.” It is to play within an environment that we recognize to be shifty and illusory. So rather than trying to make our world solid and predictable, and complaining when that is not the case, we could maintain the glimpses of the illusory nature of experience that arise in meditation practice, and touch in with that open illusory quality in the midst of our daily activities. That looser more open quality is the ground on which the compassionate actions of the bodhisattva can arise.” from — https://tricycle.org/trikedaily/train-your-mind-slogan-6/
Shunyata's Apprentice 
Still don’t quite get what a child of illusion is
Hi! I tried to respond earlier so if this is a duplicate I apologize. Not so swift at blogging on my mobile! Anyway, I’m not really sure what that means, but I think it’s something like this: in everyday life, try to remember that your Self is just constructed by stringing together all your experiences, which (in absolute terms) are not real, but only an illusion. That illusion creates (births the child) the myth of this solid, really existing entity we call the Self.
Audrey, there are some teachers doing things about the Lojang online now, though I can’t remember who. It was a pretty obscure, or at least not widely-shared, teaching for a long time, but I think they’re opening on it now. I’ll look around and see if I find more resources. It’s a wonderful text and has been a really helpful teaching in understanding life for me.
Ah-ha! Judith Leif says: “In this slogan, the particular postmeditation practice is to “be a child of illusion.” It is to play within an environment that we recognize to be shifty and illusory. So rather than trying to make our world solid and predictable, and complaining when that is not the case, we could maintain the glimpses of the illusory nature of experience that arise in meditation practice, and touch in with that open illusory quality in the midst of our daily activities. That looser more open quality is the ground on which the compassionate actions of the bodhisattva can arise.”
https://tricycle.org/trikedaily/train-your-mind-slogan-6/