With the current study we aim at gaining understanding on the properties of radio emission and the assumed jet from four radio loud and {gamma}-ray loud Narrow Line Seyfert 1 galaxies i.e. Seyfert 1 galaxies with emission lines at the low-end of the FWHM distribution. The ultimate goal is twofold; first, the investigation whether a relativistic jet is operating at the source giving out the radio output observed and second, the quantification of the jet characteristics in order to understand possible similarities and differences with the jets found in typical blazars. The current study relies on the most systematic monitoring of radio loud and {gamma}-ray detected Narrow Line Seyfert 1 galaxies in the cm and mm radio bands conducted with the Effelsberg 100-m and IRAM 30-m telescopes. It covers the longest time baselines and the most radio frequencies, to date. This dataset of multi- wavelength, long-term radio light curves is analysed from a number of perspectives. A novel algorithm is introduced in order to extract sensible variability parameters (mainly amplitudes and timescales) which are then used for the computation of variability brightness temperatures and the corresponding Doppler factors. The jet powers are computed from the light curves to estimate the energy output and compare it with typical blazars. The dynamics of radio Spectra Energy Distributions are examined for understanding the mechanism causing the variability. The length of the available light curves for 3 of the 4 sources in the sample allowed a firm understanding of the general behaviour of the sources. They all display intensive variability which seems to be happening at a pace rather faster than what is generally seen in blazars. The flaring events become progressively more prominent as the frequency increases and show intensive spectral evolution indicative of shock evolution. The variability brightness temperatures and the associated Doppler factors are rather moderate implying a mildly relativistic jet. The computed jet powers show very energetic flows. The radio polarisation in one case, clearly implies the presence of a quiescent jet underlying recursive flaring activity. Finally, in one case, the sudden disappearance of a {gamma}-ray flare below some critical frequency in our band, urges for further investigation of the possible mechanism causing the evolution of broadband events. Despite the generally lower flux densities the sources appear to show all typical characteristics seen in blazars powered by relativistic jets. Intensive variability, spectral evolution across the different bands following evolutionary paths explained by traveling shocks, Doppler factors indicating mildly relativistic speeds.