Its different with every pitcher. Some kids can come back from walks and others can't. What is acceptable to a fireballer is different that what is acceptable with a finesse pitcher. At 10 my dd could walk the bases loaded and strike out the next 3. You had to hold your breath sometimes, other kids walk the bases loaded and then they start lobbing them down the middle. At 10U there is no "acceptable" number, you have to figure it out for each kid.