Young low-mass galaxies with extreme emission-line properties are ubiquitous at high redshift and they are believed to play a key role in cosmic reionisation and the early growth of galaxies at z>4-6. However, a detailed characterisation of their physical properties, critical for a better understanding of these two outstanding problems, is yet not possible. A unique population of lower-z analogues of these primeval systems, dubbed Green Pea (GP) galaxies, provide us ideal laboratories to study in larger detail the physical mechanisms driving massive star formation, feedback and chemical evolution under similar extreme conditions, thus paving the way for future JWST and ELT studies of young galaxies. In this talk, we will review recent results and lessons learned from deep observations of GP galaxies in the local universe. In particular, we will present recent high-dispersion long-slit and GMOS/IFU spectroscopy of green peas. These studies illustrate current advantages and limitations of the chemodynamical analysis for a simultaneous study of the ionised gas kinematics, chemical enrichment and the escape of ionising photons in compact low-mass starbursts, and provide new prospects for larger studies with current and future facilities.