Line breaks in TikZ nodes

Add align=center to the style if you want to use \\:

Code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{trees}
\begin{document}
\begin{tikzpicture}[
  man/.style={rectangle,draw,fill=blue!20, align=center},
  woman/.style={rectangle,draw,fill=red!20,rounded corners=.8ex, align=center},
  grandchild/.style={grow=down,xshift=1em,anchor=west,
    edge from parent path={(\tikzparentnode.south) |- (\tikzchildnode.west)}},
  first/.style={level distance=6ex},
  second/.style={level distance=12ex},
  third/.style={level distance=18ex},
  level 1/.style={sibling distance=5em}]
    % Parents
    \coordinate
      child[grow=left] {node[man,anchor=east]{Jim}}
      child[grow=right] {node[woman,anchor=west]{Jane}}
      child[grow=down,level distance=0ex]
    [edge from parent fork down]
    % Children and grandchildren
    child{node[man] {Alfred \\ 05-04-83}}
    child{node[woman] {Berta \\ 05-04-99}}
    child {node[man] {Charles \\ 05-04-77}}
    child {node[woman]{Doris \\ 05-04-80}};        
\end{tikzpicture}
\end{document}

You could try to use a table (two rows) (tabular env) in the content; though, I have no the required package to check if it would work or that is not allowed. E.g.

  \begin{tabular}{c}
     Jim \\
     DOB \\
  \end{tabular}

If \\ does not work since it was changed someway by the package, then you could try \cr, but I suppose it could not work and if it works, it is bad LaTeX (too much TeXish).