adverb taking the 'to' particle
successfully; nicely; smoothly
Adverb describing something going well or being done in a satisfactory manner. Often used with いく or やる.
仕事がうまうまと進んだ。
The work went smoothly.
彼はうまうまと試験に合格した。
He passed the exam successfully.
expression
yummy food; yum-yum
Childish or casual expression for delicious food. Often used by or to children.
今日のおやつはうまうまだよ。
Today's snack is yummy!
子どもが「うまうま！」と言って喜んだ。
The child happily said 'yum-yum!'
うまい is the standard adjective for 'delicious' or 'skillful', while うまうま is a reduplicated, more childish or adverbial form.
Reduplication of うまい (delicious, good). The adverbial sense likely developed from the idea of things going 'tastily' or 'well'.