Hello... i built a raised bed recently and mulched about 3 inches thick with leaves i collected from the forest (mostly bamboo and mango) I planted pimento and tomato seedlings, and after a few weeks they have barely grown and are looking a bit pale yellow. On looking into it i realized the stems seemed a bit sickly (see pics below). The bed has a good sandy loam soil mixed with compost, so there shouldn't be any nutrient deficiency problems. My thinking is that the mulch was too close too the stems, although i made a bit of a gap the mulch would have fallen in the whole and surrounded the stem - am i correct in this thinking?
They looked like they've "damped off". It's an issue that is common in tomato seedlings along with some other plant species. It can be caused fungus attacking young seeds and roots and can be aggravated by being in soil that is too wet.
See all that white stuff on your mulch?
That is mold, you should remove all those infected leaves then do as Kola Lofthouse recommends and mound some soil up around the stems so they will form new roots and help support the plants.
Those moldy leaves can be saved and turned into compost or true leaf mold for reuse on your garden bed(s).