In order to get unit access rights list for child users please invoke core/check_accessors command:

svc=core/check_accessors&params={"items":[<long>],
				 "flags":<bool>}

{
   "<unit_id>": {		/* unit id */
	"<acc_id>": {		/* user id */
		"acl": <uint>,		/* inherited unit access rights, they are put as mask on direct access rights,
					   if inherited access rights prohibit -- result access right prohibit */
		"dacl": <uint>		/* if flags:1 set; direct unit access rights  (set by unit owner) */
	},
	...			/* other user ids (if any) */		
    },
    ...				/* other unit ids (if requested) */
}