I will start by saying I know nothing about first base, at all. I rarely if ever played first. So first base is foreign to me. But, Glove Smith made two very small custom leather gloves for my kids, both left-handed throwers, when they were around 5 and 7 years old. They could probably make any type of glove, any size. But, those little gloves were physically heavy. So heavy it surprised me, but they used them until they outgrew them. Good luck!