「花（はな）をもたせる」is an idiom. 花（flower）here figuratively means the honor(of success), credit as the one who did a good job, fame. もたせる　means to let someone have. So, it becomes to give the honor/credit/fame to someone (in order to make a good reputation for him/her even when it's not really like that). I think the example"部下（ぶか）に花をもたせる" alucky-san gave above is the most common situation to use the idiom. In a company, when a boss and his assistant made some good achievement together, the boss often takes the credit. But if he says "Oh, no. It's my assistant who made it possible. I was just there. " The boss is「部下に花をもたせ」ています. What a good boss! lol はなやかで、うつくしくりっぱなもの =something that is はなやかですand うつくしいですandりっぱです.

あい手に () 相手　= partner 花をもたせる（ひきたてる） = 花を持たせる（はなをもたせる）　勝利や功名を相手に譲る。相手を立てる。　例：「部下に花を持たせる」 =to make the partner to have the flower (direct interpretation) =to give something over to your partner ( common meaning ) It's a Japanese Idiom , I think it's too early for elementary student to study such a phrase. はなやかで、うつくしくりっぱなもの。 = sophisticated , beautiful and splendid thing

"I hand down a flower to my love.What a colourful and extremely fair the flower is".