Abstract I thought meant something that exists as an idea, rather than a thing, like love, beauty etc.
It can be real but has no physical existence.
Maths perhaps.
It doesn't have to be difficult to understand though.
Real effectively means actual existence, not imaginary, or conceptual so I struggle to see how abstract and real can be easily combined. As per the earlier comment an imaginary friend, no matter how complex, would not be real. In that sense imaginary and real are antonyms.
Tbh I think here is one of those cases, where the writer has tried to make something sound important by choosing a more loaded word than can be justified. We've all done it, and I don't even think it is deliberate. We try to convey things but language is a slippery tool. I even get what Sriram is trying to convey and I am struggling to come up with an exactly suitable word, I think 'immaterial' is probably best but even that has connotations which aren't justified in the circumstances.
In the end, I would suggest the problem is that too much is being made of it. If we put child talks to imaginary god, that reads as an attempt to make little if it. Abstract reads as an attempt to aggrandise it. It isn't as significant as either of those and they read as attempts at spin. There is the tendency, as mentioned earlier, to treat the actions of the babes and sucklings as way more meaningful than they can support.