There's a lot of space between the two, and lot's to consider. A 50/50 split would put you in the Federal Way, Auburn, Des Moines and Kent areas. If this is short term, any of these towns would work and the rents range would be affordable as compared to further north. The closer you get to Seattle the more expensive rent tends to be.
If you think that this could go on for a few years, as school becomes an issue you might want to look into the school districts and consider where you would like your toddler to attend.
I've attached a link to the State Report Card for schools. You can compare district to district and even school to school.