Orla,
you have really linked the science content that the children can discover with the activities you have planned. Did you know we have better maps of Mars than the Earth? This is because all of Mars is visible from space, but oceans cover up much of the Earth.
This planetary map may be useful for your class:
Children’s Planetary Maps: Mars | astroEDU (iau.org)
The activity that accompanies the map is presented at a slightly too high a level for a junior class, but the children might design a flag for Mars.