There are some very good Youth 20 gauge semi auto models that are well made and reliable. The below are light enough to be held easiely but, cycle lighter loads well to help reduce some recoil.
Gun fit makes the biggest impact of felt recoil. I don't think the opeeration type of a semi auto plays any part of recoil as long all other things are equal.
Beretta AL391 Youth: This model is very thin and pretty light in weight at around 5.9 lbs. They balance with more weight towards the stock. They are Gas operated, have 3" chambers, and cycle a wide range of shells. They have an automatic magazine cutoff and a bolt lock lever. They also come with shims to adjust the fit of the stock. They are more complicated to clean compared to other models. They do go long periods between cleanings if needed. Price wise they are around $800.00.
Beretta 3901 RL: This model is wider than the AL391. They weigh around 6.5 lbs. They balance with more weight towards the stock. They are Gas operated, have 3" chambers, and cycle a wide range of shells. They have an automatic magazine cutoff but, no bolt lock lever. They also come with shims to adjust the fit of the stock. They are pretty easy to clean and can go long periods between cleanings if needed. They hold a total of four rounds and can't take an extension to hold more. The safety button is at the back of the trigger guard. Price wise they are around $650.00.
Browning Gold SL Micro: This model is similar in size to the 3901. They weigh around 6.25 lbs and balances with more weight towards the stock. They are Gas operated, have 3" chambers, and cycle a wide range of shells. This model has the speed load feature. They have shims available to adjust the stock. They are very easy to clean and can go long periods between cleanings. They hold five rounds total and can take an extension to hold more. The safety button is at the back of the trigger guard. Price wise they are around $750.00 and Browning has a $100.00 rebate on Golds.
Franchi 720 Short Stock: This model is thinner like the AL391. It weighs about 5.8 lbs and balances with more weight towards the stock. They are Gas operated, have 3" chambers, and cycle a wide range of shells. This model has an automatic magazine cutoff. It's piston can be flipped around to allow more bleed of for heavier loads. They have shims to adjust the stock. They are one of the easier semi auto models to clean and can go long periods between cleanings. They hold five rounds total and can take an extension to hold more. The safety is at the back of the trigger guard. Price wise they are around $600.00