Xavier and Anthony Gregory busked over Christmas and used the donations to buy their bikes, which were stolen last weekend.
Anthony, 9, has played the B flat cornet player for five years, and Xavier, 11, has played the violin for five years and the baritone cornet for three.
Their mother Antonia Gregory said in the past two weeks, four bikes paid for and owned by the boys had been stolen, which she described as "mean".
"You don't expect people to help themselves."
The first two bikes were stolen two weekends ago.