I usually feed younger Leos 2 crickets at a time, if they eat both quickly I'll throw another two in there. You can feed them every day or every other day. Generally, the younger they are the less crickets and more often you feed them. As they get older you can feed them more at a time less often. Remember to remove any uneaten crickets from the cage after an hour so they don't stress your geckos. Regardless of age, all geckos eat at different rates so there's no exact number of feeders they'll need you just have to observe their eating habits and adjust accordingly.
