It's possible they have poor appetites because the temperature of the tank is off. It needs to be 88-90 degrees on the floor of the warm side of the tank. Make sure they've got hiding spots to feel secure, because some leos won't eat when stressed.
Leave a bowl of mealworms in the tank at all times. A healthy baby leo can easily eat at least 10-15 a day. Make sure you gutload your mealworms too. Feed them fish flake food, 10-grain cereal, fresh veggies (except for iceberg lettuce), etc. overnight before offering them to your leos. Mealworms are more fattening than crickets, so they will help put on some weight.
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5.6 leopard geckos
chickabowwow
