Another vote for NO here.
You've organised your working life to suit YOUR family, not theirs. Your kids need you, and will definitely, at 10 and 11 be wanting different things on a Friday afternoon after school than a 1 year old.
And besides which, there are things that you already do on Fridays that mean you cannot fit in another huge responsibility (even if that's only catching up on housework and getting the groceries - can't do those with 2 1yr olds under your feet).
They have enjoyed their freedom before now, being able to go places and do things with their friends - well, you are now in the position of being able to enjoy YOUR freedom having come nearer to the other end of childhood, so you look forward to showing them what that freedom can look like in a few years time for them.
I'd echo the thoughts of others that, in 5 years time, you may have completely different circumstances. Heck, even now - what would they do if you wanted to take YOUR DC's away for a long weekend after school on Friday, or go on holidays in the summer? 
Just say No, not as a "will do unto you" response but a "my life is very full and organised, and I cannot take on additional responsibilities like caring for 2 small kids - it is VERY hard work as you are both about to find out - but what advice can I give you getting started?"