Probably a weed, but mainly checking it's not a dangerous one to pets.
Found growing next to geranium if that helps! I took countless cuttings from MiL's garden a few months ago so things are starting to kick into action now, but I think these geraniums were taken from between paving stones under an apple tree. She told me to remove bits of weeds off the cuttings before I planted them, but of course I didn't bother 
Any ideas? It's a tiny white flower with a yellow centre, and what looks like green berries. Thanks.