  Pinpointing a pulsar in its parent supernova remnant (SNR) or resulting
pulsar wind nebula (PWN) is key for understanding its formation history, and
the pulsar wind mechanism. Yet, only about half the SNRs and PWNe appear
associated with a pulsar. We aim to find the pulsars in a sample of eight known
and new SNRs and PWNe. Using the LOFAR radio telescope at 150 MHz, each source
was observed for 3 hours. We covered the entire remnants where needed, by
employing many tied-array beams to tile out even the largest objects. For
objects with a confirmed point source or PWN we constrained our search to those
lines of sight. We identify a promising radio pulsar candidate towards PWN
G141.2+5.0. The candidate, PSR J0337+61, has a period of 94 ms and a DM of 226
pc cm$^{-3}$. We re-observed the source twice with increased sensitivities of
30% and 50% but did not re-detect it. It thus remains unconfirmed. For our
other sources we obtain very stringent upper limits of 0.8-3.1 mJy at 150 MHz.
Generally we can rule out that the pulsars travelled out of the remnant. From
these strict limits we conclude our non-detections towards point-sources and
PWNe are the result of beaming and propagation effects. Some of the remaining
SNRs should host a black hole rather than a neutron star.
