Current situation: 3DC under 4 years old (so none in school yet), small 3 bed semi. We're tight for space: DH and I both WFH two or three days a week with desks in bedrooms as no other space, pram has to live folded up in dining room so barely space to get round table, tiny kitchen (no space for dishwasher/tumble dryer), one bedroom is box room, only one toilet in bathroom upstairs etc. Location nice countryside but a bit isolated, country roads often with no pavements, would end up being taxi drivers to DC when older, have to drive to office. But it is liveable although frustrating.
Potential move a few miles away: 4 bed house with home office spaces downstairs, 4 toilets (one downstairs), 3 bathrooms, decent sized kitchen, playroom, utility room, cloakroom, big hall that could leave pram in. Pretty much dream home and location except for garden which is small, but we have discovered we are too lazy for garden maintenance and couldn't afford this size of house in this location with a bigger garden. Walking distance to centre of large town, great bus service, cycling distance to my office, big housing estate so safe roads for walking/cycling, near parks. We currently have a large amount of savings.
Currently we're mortgage free. New house would involve £100k mortgage, which is less than 2x either of our single gross salaries. 25 yr mortgage fixed for 5 years is 20% of my take home, or 15% of DH take home (IE 8% of joint take home). Hard to say how secure our jobs are, location means we'd have a good choice of employers though. Current childcare costs are very high but will only go down as DC start school. We'd have a small cushion of savings (about three months of take home) but everything else is going towards the house.
YABU: you should stay put to have the extra security of being mortgage free with decent savings in cost of living crisis
YANBU: it's worth the extra risk of a smallish mortgage and using savings to get a forever home that would be much more ideal for the family