shell is the current shell from which you executed your time statement. children is a summary of all child processes started from the same shell.
user and system show the amount of CPU seconds the above processes spent in user mode and kernel mode, respectively. See https://blog.codinghorror.com/understanding-user-and-kernel-mode/ for more info.
cpu show the combined values of user and system, as a percentage of total CPU time. total shows how long ago each process was started (here in minutes:seconds.fraction).