I’m sorry for your loss 
My husband was widowed 10 years ago with two children of a similar age, and a similar age to you.
He was immediately much better off in terms of assets, because the mortgage was paid off - though you can’t sell a house and live in it, so in terms of month to month finances he was only a mortgage payment better off, and that was less than his wife was earning.
However, he also received death in service and life insurance payments, became eligible for tax credits, and widower payment.
So actually, he was better off financially. He struggled with the lump sum money - like when he needed a new car, he felt guilty being able to buy “nice things” in his mind, because his wife had died.
Over the much longer term, of course the immediate financial “gain” would have been no more than the money he lost from not having her - yes the mortgage was paid off, but they’d have paid that off anyway. Yes, he got a lump sum - but years later her pension would have been as good as that.
In purely financial terms, over time as a single person he’d have broken even.
Much love to you and your child ❤️