If it's fairly low and sprawling with weak stems it's prob hardy geranium/cranesbill (will have small purply pink flowers), if they're tall plants with one or two sturdy stems it'll be aquilegia/old lady's bonnet. I reckon anyway!
I don't think it's herb Robert, those leaves aren't the right shape, a bit too rounded. Might be one of the other geraniums though.
I'd leave it till it flowers to tell for sure... but even if it's something pretty like herb Robert, you might want to take it out. I had some appear in my garden a few years ago, thought it looked nice and left it - now it's definitely in the weed category.