tap roots out bottom of starter cubes. Transplant?

Hey guys, I have a few seedlings that are 4 days old. Tap roots on a couple have made it through the bottom of the mini rockwool cubes.

Should I transplant into larger rockwool cubes? or are they good for now?
Will roots grow outward, or will tap root keep going down?

i wouldnt transplant untill you have a huge mass of roots but thats just me... i like to set the cubes in pearlite for around a week

thanks reggae. any other opinions?