The Child and Dependent Care Credit only applies to "day care" or similar expenses you pay for your child to be cared for while you work. Your child must be under age 13 or disabled to qualify for this credit.
The Child Tax Credit is the credit for having a qualifying child dependent. For 2020, the credit was a maximum of $2000 only for children aged 16 or less as of 12/31/2020, with a phase-out at higher income. For 2021, the credit is a maximum of $3000 per child who is aged 17 or less on 12/31/2021, with a phase out at higher income. It sounds like in 2020, you qualified for $1500 for your 15 year old, and in 2021 you qualified for $2500 for your 16 year old child (after adjusting for the high income phase-out). If you got $1000 of advanced payments, the other $1500 will be added to your refund. You don't get a credit for your 19 or 20 year old child.
