Right now Porkbun has the cheapest first year at $5.66, and Porkbun the cheapest renewal at $19.05. Over three years the lowest total at one registrar is $43.76 at Porkbun.
Why does .kids cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Porkbun, .kids renews at $19.05 after a $5.66 first year. Compare the renewal and 3-year columns before you buy.