YANBU as such, no, but you'd be very unwise to make such a significant financial decision without doing loads and loads of research and number crunching. there are various issues to consider.
Regarding mortgages, yes you can fix but usually for no more than 5 years. I wouldn't consider taking one out without knowing lots more than you do atm. Interest rates are very low at the moment and have been for some time. Opinion is divided as to how long this can continue, but what we do know is that over the last century or so the average has been 8-9%. Ideally don't take out any mortgage you couldn't afford if rates went to eg 10%, just in case. If they never go that high in 25 years, or whatever the term is, great. You don't mention your deposit, but if it's relatively low eg less than 20%, you need to be prepared for the possibility of negative equity. If that happens, when your fixed term expires you won't get a good rate.
1k a month is not that much if you live in the south east. If you're in, say, Manchester, it's a lot more than you need to pay for a nice family home, so you'd need to be able to justify the extra risk. Still, it would be a good idea to look at affordability if one of you did lose your job. Would one income be enough to afford the repayments? The traditional adage is that housing costs should be no more than one third of income, so you're within that.
Regarding childcare, how many DC do you anticipate having? What are average childcare costs locally, and do your employers offer childcare vouchers? This will give you an idea how much you'll spend. You could also look at your likely maternity pay, if you intend to take ML. If you have a 1k mortgage and 2 DC in full time nursery, this is going to take up the majority of your income, if only for a short time. You might have no more than 1k a month left over- will this be enough, what are your other outgoings?
A mortgage is a gamble and there's no getting round that- you could do all the research you like and still end up getting bitten. However, nobody should make such a big decision without having done as much research as possible!