This is called tuition remission program that is very popular in private universities. However, many classes are provided for leisure, not for credit. Children, even spouse of these universities' employee can get this benefit, too. Like in JHU, each child can get 50% tuition remission upto JHU's tuition, no matter which school the child is in. If a child has both parents work in JHU, he/she can get full tuition remission. In UPenn, 75% tuition can be remitted, no matter if 1 parent or both work there.
For most state universities, child of SU employee can enjoy free tuition in that SU (may be in different campus).
For most state universities, child of SU employee can enjoy free tuition in that SU (may be in different campus).