  We introduce a Poissonization method to study the coalescent structure of
uniform samples from branching processes. This method relies on the simple
observation that a uniform sample of size $k$ taken from a random set with
positive Lebesgue measure may be represented as a mixture of Poisson samples
with rate $\lambda$ and mixing measure $k \mathrm{d} \lambda/ \lambda$. We
develop a multitype analogue of this mixture representation, and use it to
characterise the coalescent structure of multitype continuous-state branching
processes in terms of random multitype forests. Thereafter we study the small
time asymptotics of these random forests, establishing a correspondence between
multitype continuous-state branching proesses and multitype
$\Lambda$-coalescents.
