Very useful number facts, up there with times tables. If number bonds to 10 are known it can help with SOOO many other areas of maths.
I work with a special needs group who are quite poor at maths and in the summer we had a big push at learning number bonds. Their maths has improved tremendously. Their are lots of games on the internet. topmarks.co.uk is a good site. Or you can play games with playing cards to find pairs to make 10. Or snap with pairs that make 10 (just take out the picture cards)
Once you get number bonds they are the building blocks for all number work. A good way of learning them is to have 10 pegs on a coat hanger and divide the pegs up so that there is a gap between them, so, say, three on one side and seven on the other - then turn the hanger around so that your DC can see that there are seven on one side and three on the other - that each number bond has an "opposite" pair, so:
yes, not so much learning by rote as practising lots of different activities so that these number bonds just come automatically to the child (like tables in that way). You want to get to the stage where the child 'just knows' as a fact that 8+2 is 10 and responds immediately.
Then they will learn number bonds to 20.
And once you know number bonds to 10 and 20, many other areas of maths in the future will be so much easier.